Hormones and Heredity Part 4

The White Leghorn c.o.c.k was killed and dissected on May 13, 1911, nine months after castration. I found an oval body of dark, dull brown colour loose among the intestines: this was evidently the left testis which was separated from its natural attachment and lost in the abdomen at the time of the operation. I examined the natural sites of the testes: on the right side there was a small testis of considerable size, about half an inch in diameter. When a portion of this was teased up and examined under the microscope moving spermatozoa were seen, but they were not in swarms as in a normal testis, but scattered among numerous cells. On the left side was a much smaller testis, in the tissue of which I with difficulty detected a few slowly moving spermatozoa. The vasa deferentia were seen as white convoluted threads on the peritoneum, but contained no spermatozoa.

On July 29, 1911, a little more than eleven months after the operation, I examined and killed the second of these castrated c.o.c.ks, the speckled mongrel-bred bird. I measured the comb and wattles while it was alive, in case there might be reduction in the size of these appendages when the bird was killed. The comb was 1-1/3 inches high by 2-3/8 inches in length.

The spurs were 1 inch long, curved and pointed. Saddle hackles short, hanging only a little below the end of the wing. Neck hackles well developed, similar to those of an entire c.o.c.k. Longest tail feather 15-5/8 inches, blue-black in colour.

I had no entire c.o.c.k of same breed, but measured the entire White Leghorn for comparison. Comb 1-3/4 inches high by 3-3/4 inches in length. (It is to be remembered that the comb and wattles are especially large in Leghorns.) Wattle 1-1/4 inches in vertical length. Spur 1 inch long, stouter and less pointed than in the capon. Longest tail feather 12 inches long.

When killed the capon was found to be very fat: there were ma.s.ses of fat around the intestines and under the peritoneum, which made it impossible to make out details such as ureter and vas deferens properly. I found a white nodule about half an inch in diameter attached to mesentery. The liquid pressed from this was swarming with spermatozoa in active motion.

Two other ma.s.ses about the same size or a little larger were found on the sites of the original testes. These also were full of mobile spermatozoa, and must have grown from portions of the testes left behind at castration.

In ducks the s.e.xual characters of the male differ from those in the fowl, especially in the fact that they almost completely disappear after the breeding season and reappear in the following season. In the interval the drake pa.s.ses into a condition of plumage in which he resembles the female; and this condition is known as 'eclipse.' The male plumage, therefore, in the drake has a history somewhat similar to that of the antlers in deer.

Two investigations of the effects of castration on ducks and drakes have been recorded. H. D. Goodale [Footnote: 'Castration of Drakes.' _Biol.

Bulletin_, Wood's Hole, Ma.s.s., vol. xx., 1910] removed the generative organs from both drakes and ducks of the Rouen breed, which is strongly dimorphic in plumage. One drake was castrated in the early spring of 1909 when a little less than a year old. This bird did not a.s.sume the summer plumage in 1909, that is, did not pa.s.s into eclipse. It was in the nuptial plumage when castrated. This breeding or nuptial plumage is well known: it includes a white neck-ring, brilliant green feathers on the head, much claret on the breast, brilliant metallic blue on the wing, and two or more upward curled feathers on the tail. The drake mentioned above was accidentally killed in the spring of 1910. Another drake was castrated on August 8, 1909: only the left testis was removed, the other being ligatured. At this time the bird would be in eclipse plumage. It appears from the description that it a.s.sumed the nuptial plumage in the winter of 1909, and did not pa.s.s into eclipse again in the summer of 1910. Thus in drakes the effect of castration is that the secondary s.e.xual character remains permanently instead of being lost and renewed annually. Goodale, however, does not describe the moults in detail. In the natural condition the drake must moult twice in the year, once when he sheds the nuptial plumage, and again when he drops the summer dress. Goodale insists, from some idea about secondary s.e.xual characters which is not very obvious, that the eclipse or summer plumage is not the same as that of the female.

He states that the male in summer plumage merely mimics the female but does not become entirely like her. In certain parts of the body there are no modifications toward the female type. In others, i.e. head, breast, and keel region, the feathers of the male become quite like those of the female. 'It can hardly be maintained that this is an example of a.s.sumption by the male of the female's plumage, especially as the presence of the testis is necessary for its appearance.' The idea here seems to be that since the eclipse plumage is only a.s.sumed when the testis is present, therefore it must be a male character.

Out of five females on which the operation was performed only two lived more than a few days afterwards. One of these (a) was castrated in the spring of 1909 when a little less than a year old, the other (b) on August 13 when twelve weeks old. In October 1909 they showed no marked modifications. In July 1910 it was noticed that they had the male curled feathers in the tail, and (a) had breast feathers similar to those of the male in summer plumage, (b) was rather more strongly modified: she had a very narrow white neck-ring, and breast feathers distinctly of male type.

The next moult began in September, and in November was well advanced. On the whole (a) had made little advance towards the male type, but (b) closely resembled the male in nuptial plumage. It had brilliant green feathers on the head, a white neck-ring, much claret colour on the breast, and some feathers indistinguishable from those of the male, and also the male s.e.x feathers on the tail. Goodale concludes that the female owes her normal colour to the ovaries or something a.s.sociated with them which suppresses the male characters and ensures the development of her own type. He considers it is quite as conceivable that selection should operate to pick out inconspicuously coloured females as that selection of brilliantly coloured males should bring about an addition to the female type. But as pointed out above, selection cannot explain the dimorphism in either case.

It may be mentioned here that owing to the fact that the single (left) ovary in birds is very closely attached to the peritoneum immediately covering the great post-caval vein, it is generally impossible to remove the whole of the ovary without cutting or tearing the wall of the vein and so causing fatal hemorrhage. The above results observed by Goodale are therefore all the more remarkable, and it may be a.s.sumed that he removed at any rate nearly all the ovary.

The research of Seligmann and Shattock [Footnote: Relation between Seasonal a.s.sumption of the Eclipse Plumage in the Mallard _(Anas boscas_) and the Functions of the t.e.s.t.i.c.l.e.' _Proc. Zool. Soc._ 1914.] begins with a comparison between the stages of the development of the nuptial plumage and the stages of spermatogenesis. In the young pheasant the male plumage is fully developed in the autumn of its first year, but no pairing occurs and no s.e.xual instinct is exhibited till the following spring. The wild duck pairs in autumn or early winter, after the a.s.sumption of the nuptial plumage, but copulation does not occur till spring is advanced. The investigation here considered was made upon specimens of semi-domesticated _Anas boscas_, such as are kept in London parks and supplied from game farms. The testes attain their maximum size during the breeding season-- end of March or beginning of April. At this time each organ is almost as large as a pigeon's egg, is very soft, and the liquid exuding from it when cut is swarming with spermatozoa. The bird is of course in full nuptial plumage. By the end of May, although the plumage is unchanged, the testes have diminished to the size of a haricot bean, and spermatogenesis has ceased. They diminish still further during June, July, and August, and acquire a yellow or brownish colour, while microscopically there is no sign of activity in the spermatic cells. The change from nuptial plumage to eclipse takes place between the beginning of June and the middle of July. The reappearance of the nuptial plumage takes place in the month of September, and while this process takes place there is no sign of change or renewed activity in the testes. During October and November, when the brilliant plumage is fully developed, the testes increase slowly in size but remain yellow and firm and exude no liquid on incision.

Spermatogenesis does not commence until the end of November or beginning of December. The testes increase greatly in size in January and February, and again reach their maximum size by the end of March. It is shown, therefore, that the loss of the nuptial plumage takes place in June when spermatogenesis has ceased and the testes are diminis.h.i.+ng in size, but the redevelopment of this plumage takes place in September without any renewed activity of the testis and long before the beginning of spermatogenesis.

The case of the antlers in the stag is probably very similar.

The important statement is made with regard to castration (under anaesthetics, of course) that it was found impossible to extirpate the testes completely. When the bird was killed some months after the operation, a greater or lesser amount of regenerated testicular tissue was found either on the original site of the organs or engrafted upon neighbouring organs. This experience, it will be noted, agrees with my own in the case of fowls. There were, however, reasons for believing that the results observed within the first six or eight months after the operation are not much different from those which would follow complete castration.

Castration carried out when the drake was in nuptial plumage produced the same effect which was observed by Goodale, namely, delay, and imperfection in the a.s.sumption of the eclipse condition, but the observations of Seligmann and Shattock are more precise and detailed. One example described was castrated in full winter plumage in December 1906. On July 11, when normally it would have been in eclipse, the nuptial plumage was unmodified except for a diffuse light-brown coloration on the abdomen, which is stated to be due not to any growth of new feathers but to pigmentary modification in the old. By September 1 this bird was almost in eclipse but not quite; curl feathers in the tail had disappeared, the breast was almost in full eclipse, the white ring was slightly indicated at the sides of the neck, the top of the head and the nape had still a good deal of gloss. After this the nuptial plumage developed again, and on November 12 the bird was in full nuptial plumage, with good curl feathers in the tail. The only trace of the eclipse was the presence of a few brown feathers on the flanks. This bird was killed July 30, 1908, when the bird was in eclipse, but not perfectly so, as there were vermiculated feathers mixed with eclipse feathers on the breast, abdomen, and flanks. Dissection showed on the right side a series of loosely attached nodular grafts of testicular tissue, in total volume about the size of a haricot bean: on the left side two small nodules, together about the size of a pea, and two other grafts at the root of the liver and on the mesentery. Several other cases are described, and the general result was that the eclipse was delayed and never quite complete, while although the nuptial plumage was almost fully developed in the following winter, it retained some eclipse feathers, and was also delayed and developed slowly.

Several drakes were castrated in July when in the eclipse condition, and although the authors state, in their general conclusions, that this does not produce any constant appreciable effect upon the next pa.s.sage of the bird into winter plumage, they describe one bird so treated which on November 18 retained many eclipse feathers: the general appearance of the chestnut area of the breast was eclipse.

It must be remembered that not only was the castration in these cases incomplete, but also that it was performed on mature birds. Birds differ from Mammals, firstly, in the difficulty of carrying out complete castration, and secondly, in the fact that the occurrence of p.u.b.erty is not so definite, and that immature birds are so small and delicate that it is almost impossible to operate upon them successfully.

a.s.sUMPTION OF MALE CHARACTERS BY THE FEMALE

That male somatic s.e.xual characters are latent in the female is shown by the frequent appearance of such characters in old age, or in individual cases. The development of hair on the face of women in old age, or after the child-bearing period, is a well-known fact. Rorig, [Footnote: 'Ueber Geweihbildung und Geweihentwicklung.' _Arch. Ent.-Mech._ x. and xi.] who carefully studied the antlers of stags, states that old sterile females, and those with diseased ovaries, develop antlers to some degree. Cases of crowing hens, and female birds a.s.suming male plumage have long been known, but the exact relation of the somatic changes to the condition of the ovaries in these cases is worthy of consideration in view of the results obtained by Goodale after removal of the ovaries from ducks. Shattock and Seligmann [Footnote: 'True Hermaphroditism in Domestic Fowl, etc.' _Trans.

Path. Soc._, Lond., 57. 1, 1906.] record the case of a gold pheasant hen which a.s.sumed the full male plumage after the first moult: it had never laid eggs or shown any s.e.xual instincts. The only male character which was wanting was that of the spurs. The ovary was represented by a smooth, slightly elevated deep black eminence 1 cm. in length and 1-5 mm. in breadth at its upper end. These authors also mention three ducks in male plumage in which the ovary was similarly atrophied but not pigmented. They regard the condition of the ovary as insufficient to explain the development of the male characters, and suggest that such birds are really hermaphrodite, a male element being possibly concealed in a neighbouring organ such as the adrenal or kidney. This hypothesis is not supported by observation of testicular tissue in any such case, but by the condition found in a hermaphrodite specimen of the common fowl described in the paper. This bird presented the fully developed comb and wattles and the spurs of the c.o.c.k, but the tail was quite devoid of curved or sickle feathers, and resembled that of the hen. Internally there were two oviducts, that of the left side normally developed, that of the right diminutive and less than half the full length. The gonad of the left side had the tubular structure of a testis, but showed no signs of active spermatogenesis, but in its lower part contained two ova. The organ of the right side was somewhat smaller, it had the same tubular structure, and in one small part the tubules were larger, showed division of nuclei (mitotic figures), and one of them showed active spermatogenesis.

In discussing Heredity and s.e.x in 1909, [Footnote: _Mendel's Principles of Heredity_. Camb. Univ. Press, 1909.] Bateson referred to the effects of castration as evidence that in different types s.e.x may be differently const.i.tuted. Castration, he urged, in the male vertebrate on the whole leads merely to the non-appearance of male features, not to the a.s.sumption of female characters, while injury or disease of the ovaries may lead to the a.s.sumption of male characters by the female. This was supposed to support the view that the male is h.o.m.ozygous in s.e.x, the female heterozygous in Vertebrates: that is to say, the female s.e.x-character and the female secondary s.e.x-characters are entirely wanting in the male. This argument a.s.sumes that the secondary characters are essentially of s.e.xual nature without inquiring how they came to be connected with s.e.x, and it ignores the fact that the influence of castration on such characters is a phenomenon entirely beyond the scope of Mendelian principles altogether.

The fact that castration does affect, in many cases very profoundly, somatic characters confined to one s.e.x, proves that Mendelian conceptions, however true up to a certain point, are by no means the whole truth about heredity and development. For it is the essence of Mendelism as of Weismannism that not only s.e.x but all other congenital characters are determined in the fertilised ovum or zygote. The meaning of a recessive character in Mendelian terminology is one that is hidden by a dominant character, and both of them are due to factors in the gametes, particularly in the chromosomes of the gametes which come together in fertilisation. For example, in fowls rose comb is dominant over single. A dominant is something present which is absent in the recessive: the rose comb is due to a factor which is absent from the single. The two segregate in the gametes of the hybrid or heterozygote, and if a recessive gamete is fertilised by another recessive gamete the single comb reappears. But castration shows that the antlers of stags and other such characters are not determined in the zygote when the s.e.x is determined, but owe their development, partly at least, to the influence of another part of the body, namely, the testes during the subsequent life of the individual.

According to Mendelism the structure and development of each part of the soma is due to the const.i.tution of the chromosomes of the nuclei in that part. The effects of castration show that the development of certain characters is greatly influenced in some way by the presence of the testes in a distant part of the body. The Mendelians used to say it was impossible to believe in the heredity of somatic modifications due to external conditions, because it was impossible to conceive of any means by which such modifications could affect the const.i.tution of the chromosomes in the gametes within the modified body. It would have been just as logical to deny the proved effects of castration, because it was impossible to conceive of any means by which the testes could affect the development of a distant part of the body.

But this is not all. The supposed fact that female secondary characters in Vertebrates are absent in the male is completely disproved for Mammals by the presence of rudimentary mammary glands in the male. It is true that secondary s.e.x-characters are usually positive in the male, while those of the female are apparently negative, but in the case of the mammary glands the opposite is the case. There is no room for doubt that the mammary glands are an essentially female somatic s.e.x-character, not only in their function but in the relation between the periodicity of that function and those of the ovaries and uterus, and it is equally certain from their presence in rudimentary condition in the male that they are not absent from the male const.i.tution.

INFLUENCE OF GONADS DUE TO HORMONES

The existence and the influence of hormones or internal secretions may be said to have been first proved in the case of the testes, for Professor A.

A. Berthold [Footnote: 'Transplantation der Hoden,' _Archiv. f Anat. u.

Phys._, 1849.] of Gottingen in 1849 was the first to make the experiment of removing the t.e.s.t.i.c.l.es from c.o.c.ks and grafting them in another part of the body, and finding that the animals remained male in regard to voice, reproductive instinct, fighting spirit, and growth of comb and wattles. He also drew the conclusion that the results were due to the effect of the t.e.s.t.i.c.l.e upon the blood, and through the blood upon the organism. Little attention was paid to Berthold's experiment at the time. The credit of having been the first to formulate the doctrine of internal secretion is generally given to Claude Bernard. He discovered the glycogenic function of the liver, and proved that in addition to secreting bile, that organ stores up glycogen from the sugar absorbed in the stomach and intestines, and gives it out again as sugar to the blood. In 1855 he maintained that every organ of the body by a process of internal secretion gives up products to the blood. He did not, however, discover the action of such products on other parts or functions of the body. Brown-Sequard, in his address before the Medical Faculty of Paris in 1869, was the first to suggest that glands, with or without ducts, supplied special substances to the blood which were useful or necessary to the normal health, and in 1889 at a meeting of the Societe de Biologie he described the experiment he had made upon himself by the injection of testicular extract. This was the commencement of organotherapy. Since that time investigation of the more important organs of internal secretion--namely, the gonads, thyroid, thymus, suprarenals, pituitary, and pineal bodies--has been carried on both by clinical observation and experiment by a great number of physiologists with very striking results, and new hormones have been discovered in the walls of the intestine and other organs.

Here, however, we are more especially concerned with the gonads and other reproductive organs. A great deal of evidence has now been obtained that the influence of the testes and ovaries on secondary s.e.xual characters is due to a hormone formed in the gonads and pa.s.sing in the blood in the course of the circulation to the organs and tissues which const.i.tute those characters. The fact that transplanted portions of testes in birds (c.o.c.ks and drakes) are sufficient to maintain the secondary characters in the same condition as in normal individuals shows that the nexus between the primary and somatic organs is of a liquid chemical nature and not anatomical, through the nervous system for example. Many physiologists in recent years have maintained that the testicular hormone is not derived from the male germ-cells or spermatocytes, but from certain cells between the spermatic tubuli which are known as interst.i.tial cells, or collectively as the interst.i.tial gland.

The views of Ancel and Bouin, [Footnote: _C. R. Soc. Biol., iv._]

published in 1903, may be described in large part as theory. They state that the interst.i.tial cells appear in the male embryo before the gametocytes present distinctive s.e.x-characters. They conclude that the interst.i.tial cells supply a nutritive material (hormone?), which has an effect on the s.e.xual orientation of the primitive generative cells. In addition to this function, the interst.i.tial cells by their hormone also give the s.e.xual character to the soma. When castration is carried out at birth the male somatic characters do not entirely disappear, because the hormone of the interst.i.tial cells has acted during intrauterine life. The functional independence between the interst.i.tial cells and the seminal tubules is shown by the fact that if the vasa deferentia are closed the seminal gland (_i.e._ tubules) degenerates while the interst.i.tial cells do not. In the embryo the interst.i.tial gland is large, in the adult proportionately small.

There is complete disagreement between the results of Ancel and Bouin on the one hand, and those of Shattock and Seligmann on the other, with regard to the effects of ligature of the vasa deferentia. The latter authors, as mentioned above, found that after ligature not only the somatic characters but the testis itself developed normally. The experiments were performed on Herdwick sheep and domestic fowls. They state that on examination the testes were found to be normally developed, and spermatogenesis was in progress. The experiments of Ancel and Bouin were carried out on rabbits seven to eight weeks old, and consisted in removing one testis, and ligaturing the vas deferens of the other. About six months after the operation the testis left _in situ_ was smaller, the seminal tubules contained few spermatogonia, though Sertoli's cells (cells on the walls of the tubules to which the true spermatic cells are attached) were unchanged; while the interst.i.tial cells were enormously developed, by compensatory hypertrophy in consequence of the removal of the other testis. At the same time the male instincts and the other generative organs were unchanged. In a few cases, however, Ancel and Bouin observed atrophy of the interst.i.tial cells as well as the spermatic cells.

They believe this is due to the nerves supplying the testis being included in the ligature. This is rather a surprising conclusion in view of the fact that testicular grafts show active spermatogenesis. It is difficult to understand why nerve connection should be necessary for the interst.i.tial cells and not for the spermatic, and, moreover, if the interst.i.tial cells are really the source of the hormone on which the somatic characters depend, they must be acting in the grafts in which the nerve connections have been all severed.

The facts concerning cryptorchidism, that is to say, failure of the descent of the testes in Mammals, seem to show that the hormone of the testis is not derived from s.e.m.e.n or spermatogenesis, for in the testes which have remained in the abdomen there is no spermatogenesis, while the interst.i.tial cells are present, and the animals in some cases exhibit normal or even excessive s.e.xual instinct, and all the male characteristics are well marked. It may be remarked, however, in criticism of this conclusion that the descent of the testes being itself a somatic s.e.xual character of the male, its failure when the interst.i.tial cells are normal and the spermatic cells defective, would rather tend to prove that the defect of the latter is itself the cause of cryptorchidism.

Many investigators have found that the Rontgen rays destroy the spermatic cells of the testis in Mammals, leaving the cells of Sertoli, the interst.i.tial tissue, nerves, and vessels uninjured. Tandler and Gross [Footnote: _Wiener klinische Wochenschrift_, 1907.] found that the antlers of roebuck were not affected after the testes had been submitted to the action of the rays, showing that the interst.i.tial cells were sufficient to maintain the normal condition of the antlers. Simmonds, [Footnote: _Fortschr. a. d. G. d. Rontgenstr._, xiv., 1909-10.] however, found that isolated seminal tubules remained, and regeneration took place, and concludes that both spermatic cells and interst.i.tial cells take part in producing the testis hormone. The conclusions of two other investigators have an important bearing on this question--namely, that of Miss Boring [Footnote: _Biol. Bull._, xxiii. 1912.] that there is no interst.i.tial tissue in the bird's testis, and that of Miss Lane-Claypon, [Footnote: _Proc. Roy. Soc._, 1905] that the interst.i.tial cells of the ovary arise from the germinal epithelium, and are perfectly equipotential with those which form the ova and Graafian follicles. It seems possible, although no such suggestion has been made, that the interst.i.tial cells might either normally or exceptionally give rise to ova and spermatocytes. The observations of Seligmann and Shattock on the relation of spermatogenesis to the development of nuptial plumage in drakes probably receive their explanation from the above facts. Spermatogenesis is not the only source of the testicular hormone: changes in the secretory activity of the interst.i.tial cells or spermatocytes are sufficient to account for periodic development of somatic s.e.x-characters, and the same reasoning applies to the antlers of stags.

THE MAMMARY OR MILK GLANDS

The milk glands in Mammals const.i.tute one of the most remarkable of secondary s.e.xual characters. Except in their functional relations to the primary organs, the ovaries, and to the uterus, there is nothing s.e.xual about them. They are parts of the skin, being nothing more or less than enormous enlargements of dermal glands, either sebaceous or sudoriparous.

Uterine and mammary functions are generally regarded as essentially female characteristics, and are included in the popular idea of the s.e.x of woman.

Scientifically, of course, they are not at all necessary or universal features of the female s.e.x, but are peculiar to the mammalian cla.s.s of Vertebrates in which they have been evolved. Milk glands, then, are somatic s.e.x-characters common to a whole cla.s.s, instead of being restricted to a family like the antlers in Cervidae. There is not the slightest trace or rudiment of them in other cla.s.ses of Vertebrates, such as Birds or Reptiles. They are not actually s.e.xual in their nature, since their function is to supply food for the young, not to play a part in the relations of the s.e.xes. What is s.e.xual about them is--firstly, that they are normally fully developed only in the female, rudimentary in the male; secondly, that their periodical development and functional activity depends on the changes which take place in the ovary and uterus. Many investigators have endeavoured to discover the nature of the nexus between the latter organs and the milk glands.

That this nexus is of the nature of a hormone is generally agreed, and may be regarded as having been proved in 1874 when Goltz and Ewald [Footnote: _Pflugers Archiv,_ ix., 1874.] removed the whole of the lumbo-sacral portion of the spinal cord of a b.i.t.c.h and found that the mammae in the animal developed and enlarged in the usual way during pregnancy and secreted milk normally after parturition. Ribbert [Footnote: _Fortschritte der Medicin,_ Bd. 7.] in 1898 transplanted a milk gland of a guinea-pig to the neighbourhood of the ear, and found that its development and function during pregnancy and at parturition were unaffected. The effective stimulus, therefore, is not conveyed through the nervous system, but must be a chemical stimulus pa.s.sing through the vascular system.

Physiologists, however, are not equally in agreement concerning the source of the hormone which regulates lactation. Starling and Miss Lane-Claypon concluded from their experiments on rabbits that the hormone originated in the foetuses themselves within the pregnant uterus. In virgin rabbits it is difficult to find the milk glands at all. When found the nipple is minute and sections through it show the gland to consist of only a few ducts a few millimetres in length. Five days after impregnation the gland is about 2 cm. in diameter. Nine days after impregnation the glands have grown so much that the whole inner surface of the skin of the abdomen is covered with a thin layer of gland tissue. In six cases by injecting subcutaneously extracts of foetus tissue Starling and Lane-Claypon obtained a certain amount of growth of the milk glands. The hormone in the case of the pregnant rabbit is of course acting continuously for the whole period of pregnancy, while the artificial injection took place only once in twenty-four hours, and the amount of hormone it contained may have been absorbed in a very short time. The amount of growth obtained experimentally in five weeks was less than that occurring in pregnancy in nine days. Extracts of uterus, placenta, or ovary produced no growth, although the ovaries used were taken from rabbits in the middle of pregnancy. In one experiment ovaries from a pregnant rabbit were implanted into the peritoneum of a non-pregnant rabbit, but on post-mortem examination of the latter eleven days later the implanted ovaries were found to be necrosed and no proliferation of milk gland had taken place.

The conclusions of Starling and Lane-Claypon were confirmed by Foa, [Footnote: _Archivo d. Fisiologia_, v., 1909.] and by Biedl and Konigstein, [Footnote: _Zeitschrift f. exp. Path. und Therap_., 1910.] Foa states that extracts of foetuses of cows produced swelling of the mammae in a virgin rabbit.

O'Donoghue, however, concludes from a study of the Marsupial _Dasyurus_ that the stimulus which upon the milk glands proceeds from the corpora lutea in the ovary. In this animal changes in the pouch occur in pregnancy, which are doubtless also due to hormone stimulation, but which we will not consider here. The most important evidence in O'Donoghue's paper [Footnote: _Quart. Journ. Mic. Sci_., lvii., 1911-12.] is that development of the milk glands takes place after ovulation not succeeded by pregnancy; that is to say, when corpora lutea are formed but no fertilised ova or foetus are present in the uterus. In one case eighteen days after heat, the milk gland was in a condition resembling that found in the stages twenty-four and thirty-six hours after parturition. In another specimen, twenty-one days after heat, the milk glands were still more advanced, with distended alveoli and enlarged ducts. The alveoli contained a secretion which was almost certainly milk, O'Donoghue states that the entire series of growth changes in these animals up to twenty-one days after heat in identical with that which occurs in normally pregnant animals.

O'Donoghue's conclusion is in agreement with that of Basch,[Footnote: _Monatesschr. f. Kinderh. V._, No. ix., Dec. 1909.] who states that implantation of the, ovaries from a pregnant b.i.t.c.h under the skin of the back of a one-year-old b.i.t.c.h that was not pregnant was followed by proliferation of the mammary glands of the latter. After six weeks the glands were considerably enlarged, and after eight weeks they were caused to secrete milk by the injection of extract of the placenta. It has to be remembered, however, that the milk glands undergo considerable growth, especially in the human species, at p.u.b.erty and at every menstruation, or at oestrus in animals, which correspond to menstruation. In these cases there is no question of any influence of the foetus, and experiment has shown that if the ovaries are removed before p.u.b.erty, the milk glands nor the uterus undergo the normal development and menstruation does not occur.

According to Marshall to Jolly [Footnote: _Quart. Journ. Exp. Phys._, i.

and ii., 1906.] the symptoms of oestrus in castrated b.i.t.c.hes were found to result from the implantation of ovaries from other individuals in the condition of oestrus.

Before considering further the question of the corpora lutea as organs of internal secretion, we may briefly refer to the origin and structure of these bodies and of other parts of the mammalian ovary. The mature follicle containing the ovum differs from that of other Vertebrates in the fact that it is not completely filled by the ovum and the follicular cells surrounding it, but there is a cell-free s.p.a.ce of large size into which the ovum covered by follicular cells projects. In the wall of the follicle two layers are distinguished, the theca externa, which is more fibrous, and the theca interna, which is more cellular. In the connective tissue stroma of the ovary between the follicles are scattered, or in some cases aggregated, epithelioid cells known as the interst.i.tial cells, and it is stated that the cells of the theca interna are exactly similar to the interst.i.tial cells. According to Limon [Footnote: _Arch. d'Anat. micr._, v., 1902.] and Wallart [Footnote: _Arch. f. Gynock_, vi. 271.] the interst.i.tial cells are actually derived from those of the theca interna of the follicles. Numbers of ova die without reaching maturity, the follicular cells degenerate, and the follicle becomes filled with the cells of the theca interna, which have a resemblance to those of the true corpus luteum. These degenerate follicles have been termed spurious corpora lutea, or atretic vesicles. The interst.i.tial cells are the remains of these atretic vesicles. The true corpora lutea arise from follicles in which the ova have become mature and from which they have escaped through the surface of the ovary. As a result of the escape of the ovum and the contents of the cell-free s.p.a.ce, the follicle contracts and the follicular (so-called granulosa) cells secrete a yellow substance, lutein, and enlarge. Buds from the theca interna invade the follicle and form the connective tissue of the corpus luteum.

Somewhat similar processes take place in the ovaries of Teleostean fishes, as I know from my own observations, but no corpora lutea are formed in these, although the degenerating follicles in course of absorption correspond to corpora lutea. The sp.a.w.ning of Fishes, usually annual, corresponds to ovulation in Mammals, and in the ovary after sp.a.w.ning the numerous collapsed follicles containing the follicular cells may be seen in all stages of absorption. [Footnote: Cunningham, 'Ovaries of Teleosteans.' _Quart. Journ. Mic. Sci._, vol. xl. pt. 1., 1897.] At other times of the year sections of the ovary show here and there ova which after developing to a certain stage die and undergo absorption with their follicles.

In the higher Mammals (Eutheria) the corpora lutea show a special relation in their development to the occurrence of pregnancy, that is to say, they have a different history when ovulation is followed by pregnancy to that which they have when the ova, from the escape of which they arise, are not fertilised. When fertilisation occurs the corpus luteum increases in size during the first part of the period of gestation (four months, or nearly a half of the whole period in the human species). It then remains without much change till parturition, after which it shrinks and is absorbed. When pregnancy does not occur the corpus luteum is formed, but begins to diminish within ten or twelve days in the human species and is then gradually absorbed. According to O'Donoghue, in the Marsupial _Dasyurus_ there seems to be no difference either in the development of the milk glands or of the corpora lutea between the pregnant and the non-pregnant animal. Sandes [Footnote: _Proc. Lin. Soc._, New South Wales, 1903.]

showed that in the same species the corpora lutea persisted not only during the whole of pregnancy, which Professor J. P. Hill [Footnote: _Anat. Anz._, xviii., 1900.] estimates at a little over eight days, but during the greater part of the period of lactation, which according to the same authority is about four months. In the specimens of _Dasyurus_ described by O'Donoghue, in which the milk glands developed after ovulation without ensuing pregnancy, normally developed corpora lutea were present in the ovary. Of the five females which he mentions, the first three, one with unfertilised ova in the uteri, two five and six days after heat, could not have been pregnant, but the other two killed eighteen and twenty-one days after heat might, since pregnancy lasts only eight days, have been pregnant, the young having died at parturition or before. To make certain on this point it would have been necessary to examine the ovaries and milk glands of females which had been kept separate from a male the whole time. There is no doubt, however, about the development of the milk glands in the first three specimens, which were certainly not pregnant.

It is difficult to reconcile entirely the evidence described by O'Donoghue from _Dasyurus_, with that obtained from higher Mammals, although on the whole there is reason to conclude that the corpora lutea have an important influence on the development of the milk glands. According to Lane-Claypon and Starling, if the ovaries and uteri are removed from a pregnant rabbit before the fourteenth day the development of the mammary gland ceases, retrogression takes place, and no milk appears in the gland. If, on the other hand, the operation be performed after the fourteenth day, milk appears within two days after the operation. It is to be concluded from this that the cause of _secretion_ of milk is the withdrawal of a stimulus proceeding from ovary or uterus. But O'Donoghue believes that milk is secreted in _Dasyurus_ when no pregnancy has occurred. Ancel and Bouin [Footnote: _C. R. Soc. de Biol._, t. lxvii., 1909.] have shown that the growth of the mammary glands was produced in rabbits by the artificial rupture of egg follicles and consequent production of corpora lutea: the growth of the glands continued up to the fourteenth day, after which regression set in. This shows that the development of the milk glands in rabbits is due to the corpora lutea. On the other hand, Lane-Claypon and Starling state that in rabbits the corpora lutea diminish after the first half of pregnancy, while the growth of the milk glands is many times greater during the second half than during the first half of the period, and during the second half the ovaries may be removed entirely without interfering with the course of pregnancy or the normal development of the milk glands. It is evident, therefore, that in rabbits, whatever influence the corpora lutea may have in the first half of pregnancy, they have none in the second half, and that at this period the essential hormone proceeds from the developing foetus or foetal placenta. Again, if it is the withdrawal of a hormone stimulus which changes the milk gland from growth to secretion, it cannot be the corpora lutea which are exclusively concerned even in _Dasyurus_, for they persist during lactation, while secretion begins shortly after parturition.

Gustav Born suggested, and Frankel tested the suggestion experimentally, that the corpus luteum of pregnancy is a gland of internal secretion whose function is to cause the attachment of the ovum in the uterus and the normal development of uterus and placenta. Frankel found that removal of both ovaries in rabbits between the first and sixth days after fertilisation prevented pregnancy, and that the same result followed if the corpora lutea were merely destroyed _in situ_ by galvano-cautery.

Either process carried out between the eighth and twentieth days of pregnancy causes abortion.

Lane-Claypon and Starling also found that removal of both ovaries in the rabbit before the fifteenth day was apt to cause abortion, but at a later stage the same operation could be performed without interfering with the course of pregnancy. According to these authors numberless instances prove that in women double ovariotomy does not necessarily interfere with the course of pregnancy or the development of the milk glands. Parturition may take place and be followed by normal lactation. This shows that a hormone from the corpora lutea is not necessary either to the uterus or the milk glands, at any rate in the last third of pregnancy, though of course this does not prove that such a hormone is not necessary for the earlier stages both of pregnancy and growth of the milk glands.

The results of Steinach, if confirmed, would prove conclusively that the ovaries and testes produce hormones which determine the development of all the s.e.xual characters, not merely physical but psychical. He adopts the view that the interst.i.tial cells or gland are the source of the active hormone. He claims by transplantation of the gonads in young rats and guinea-pigs to have feminised males and masculised females. The females are smaller, and hare finer, softer hair than the males. The testes were removed and ovaries implanted in young males. The animals so treated grew less than the merely castrated specimens, and therefore when full-grown resembled females in size. In the young state both s.e.xes have fine, soft hair, the feminised males had the same character, like the normal females.

They also developed teats and milk glands like the females, and were sought and treated as females by the normal males. When the implanted ovaries are able to resist the influence of their new surroundings, the female interst.i.tial gland, which Steinach calls the p.u.b.erty gland, develops so much that an intensification of the female character takes place: the animals are smaller than normal females, the milk glands develop and secrete milk, which can be easily pressed out, and if young are given to them they suckle them and show all the maternal instincts.

Why the ovary in normal circ.u.mstances only when in the gravid condition calls forth this perfection of femaleness is to be shown in a later publication. By acting with Rontgen rays on the region where the ovaries lie, Steinach and his colleague Holzknecht brought about all the symptoms of pregnancy, development of teats and milk glands, secretion of milk, and great growth of the uterus in all its layers.

Masculising of females was much more difficult than feminising of males because the testicular tissue was less resistent, and could not be grafted so easily. When it succeeded, however, degeneration of the seminal tubules took place, with increase of the interst.i.tial or Leydig's cells. The v.a.g.i.n.al opening in rats disappeared, partly or completely. The s.e.xual instincts became male, the animals recognised a female in heat from one that was not, and attempted to copulate.