Gustav Born suggested, and Fränkel 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. Fränkel 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 sexual characters, not merely physical but psychical. He adopts the view that the interstitial 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 sexes 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 interstitial gland, which Steinach calls the puberty 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 circumstances only when in the gravid condition calls forth this perfection of femaleness is to be shown in a later publication. By acting with Röntgen 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 interstitial or Leydig's cells. The vaginal opening in rats disappeared, partly or completely. The sexual instincts became male, the animals recognised a female in heat from one that was not, and attempted to copulate.
Steinach considers that he has proved from results that sex is not fixed or predetermined but dependent on the puberty gland. By sex here he obviously means the instincts and somatic characters, for sex in the first instance, as we have already pointed out, means the difference between ovary and testis, between ova and spermatozoa. It is difficult to accept all Steinach's results without confirmation, especially those which show that the feminised male is more female than the normal female. Such a conclusion inevitably suggests that the investigator is proving too much.
The subject of the influence of hormones from the gonads is mentioned, but not fully discussed, in a volume by Dr. Jacques Loeb, entitles The Organism as a Whole. [Footnote: Putnam's Sons, 1916.] Loeb entirely omits the problem of the origin of somatic sex-characters, and fails to perceive that the fact that such characters are dependent to a marked degree on hormones derived from the gonads, together with their relation to definite habits and functions connected with the behaviour of the sexes to each other, is proof are these characters are not gametogenic, but were originally due to external stimulation of particular parts of the soma.
CHAPTER IV
Origin Of Somatic Sex-Characters In Evolution
In his Mendel's Principles of Heredity, 1909, Bateson does not discuss the nature of somatic sex-characters in general, but appears to regard them as essential sex-features, as male or female respectively. As mentioned above, he argues from the fact that injury or disease of the ovaries may lead to the development of male characters in the female, that the female is heterozygous for sex, and from the supposed fact that castration of the male leads merely to the non-appearance of male somatic characters, that the female sex-factor is wanting in the male. He does not distinguish somatic sex-characters from primary sex-factors, and discusses certain cases of heredity limited by sex as though they were examples of the same kind of phenomenon as somatic sex-characters in general. One of these cases is the crossing by Professor T. B. Wood of a breed of sheep horned in both sexes with another hornless in both sexes. In the F1 generation the males were horned, the females hornless. Here, with regard to the horned character, both sexes were of the same genetic composition, i.e. heterozygous, or if we represent the possession of horns by H, and their absence by h, both sexes were Hh. Thus Hh[male] was horned and Hh[female] was hornless, or, as Bateson expresses it, the horned character was dominant in males, recessive in females. Bateson offers no explanation of this, but it obviously suggests that some trace of the original dimorphism of the sheep in this character was retained in both horned and hornless breeds. We may suppose that the factor for horns had disappeared entirely from the hornless sheep by a mutation, but in the horned breed another mutation had been a weakening of the influence of the sexual hormones on the development of the character, which, as in all such cases, is really inherited in both sexes. In the F1, when the horned character in the female is only inherited from one side, the hereditary tendency is not enough to overcome the influence of the absence of the testis hormone and presence of the ovarian hormone, and so the horns do not develop. The Mendelian merely sees a relation of the character to sex, but overlooks entirely the question of the dimorphism in the original species from which the domesticated breeds are descended. Similarly, with regard to cattle where it has been found that hornlessness is dominant or nearly so in both sexes, no reference is made to the opposite fact that wild cattle have horns in both sexes and are not dimorphic in this character.