External Genitalia

Penis. Clitoris. Scrotum and Perineum.

(i) Before complete development. When considering this subject the period of our inquiry is not limited by the date of birth, for at this time the external generative organs in many species have not attained their permanent form. This is notably the case with mice, rats and rabbits; these animals are born in a very immature state.

Hypospadias. Oestrone when given to the mother shortly before parturition, or to the young soon after birth, may restrict in the male the growth of the scrotum and penis, so that these structures resemble those of the female in character (Lacassagne, 1934b). In the female hypospadias is readily produced. This result has been recorded by Hain (1935 a), Wiesner (1935), Greene & Ivy (1937) and Turner & Burkhardt (1939). It should be explained that normal female rats and mice possess a penis somewhat like that of the male, the urethra in both sexes terminating at the free extremity of the organ. In the condition produced by oestrogens in female rats and mice, and here described as hypospadias, there is a median ventral cleft in the penis so that the urethra opens close to the vagina, and the external genitalia conform to the pattern of those organs in the female of the human and many other species. Hain (1935 a) injected 1 mg. of oestrone into pregnant rats between the 17th and 20th days of gestation. All the female young which survived this treatment had ventral clefts of the urethra. A similar condition could be caused shortly after birth by giving oestrone to the lactating mother, the oestrogen being conveyed to the young in the milk. This result occurred after the administration of 2 mg. of oestrone to the mother during the first 4 days after parturition, or after 2 mg. were given as a single dose on the 3rd postnatal day, or after 3 mg. given during the first 2 days. Hain (1936) found that the same condition could be produced by injecting oestrone directly into the newborn young. Greene & Ivy (1937) obtained similar results in rats by injecting 2 or 3 mg. of oestradiol into the mother before parturition or 0.2 to 0.4 mg. into the newborn females.

The subsequent discussion may be easier to follow if it is preceded by a statement of what appear, from experiments on animals, to be the principal causes of mammary cancer. They are as follows:

1. I. Oestrogen.

2. II. Hereditary Factors: (a) Genie; (b) Nongenic.

3. III. Subsidiary Factors.

The Role of Oestrogen in Mammary Cancer

(a) The influence of the ovary. Long before the identification of oestrone the ovary was thought to be an agent in the development of mammary cancer. In 1896 Sir George Beatson stated that ‘we must look in the female to the ovaries as the seat of the exciting cause of carcinoma, certainly in the mamma, in all probability of the female organs generally’. Beatson's views on the causative influence of the ovaries were confirmed by experiments in the laboratory. Lathrop & Leo Loeb (1916), using female mice of several different strains, found that removal of the ovaries, if carried out before the age of 6 months, led to a pronounced decrease in the incidence of cancer of the breast in these animals, although it did not entirely prevent it. In the few cases in which cancer arose in spayed female mice, it appeared later in life than in non-spayed mice of the same strain. Spaying mice above the age of 6 months did not have any pronounced effect in preventing mammary cancer. In a second paper (1919) Loeb showed, with greater precision than before, a contrast between the results of early and late spaying. If the ovaries were removed from mice between the ages of 3 and 5 months, cancer of the mamma was almost entirely prevented. If the spaying was done between the 5th and the 7th months, the cancer rate was diminished and when cancer did appear it was at a later age on the average than in nonspayed mice. Removal of the ovaries after the 8th month of life had no appreciable effect in reducing the incidence of mammary cancer.

Cori (1927) followed up Loeb's investigations. He removed the ovaries from mice belonging to a strain in which 78 per cent of the females suffered from spontaneous mammary carcinoma. In forty-nine of these mice which had been spayed at ages varying from 2 to 6 months, and which lived to 19 months or more, mammary cancer developed in five only.

In the last few years our comprehension of vital phenomena has been rapidly extending. The nature of the sex hormones, and the reactions of living tissues toward them, have been prominent in this advance, and it is now generally understood that compounds formed in the pituitary, gonads and adrenals radically affect the structure and functions of the body and the workings of the mind. To-day our knowledge of these matters is growing so fast that to keep abreast of it is not easy for those who are occupied with.many other affairs. The author felt, therefore, that a co-ordinated summary of experimental inquiries in this field might be useful. In pursuing the idea attention has been confined almost entirely to biological work performed in the laboratory; the ultimate possibility of applying the experience so gained for the benefit of man has been the leading motive.

The essay can hardly be offered to the scientific world without an apology. Biological work is still largely confined to qualitative observation. Life is a changing process and in solving its problems we are often deprived of fixed and measurable data; moreover, the adaptability of living tissue to circumstance involves so many and such complex reactions that an exact prediction of the outcome of any extraneous influence cannot, as a rule, be stated in precise quantitative terms; nor can experimental results in this field be described adequately without specifying the conditions in which they were obtained. The presentation of the subject demanded by the latter drawback may, it is feared, be tedious to the reader, especially as the narrative contains many references to the literature. Sir James Paget complained of the difficulty of composing a readable scientific review, and the present writer is too modest to suppose that he has overcome the difficulty. It is hoped, however, that the matter contained in these pages may supply a trustworthy, though limited, foundation for further progress in both sex-hormone research and clinical practice.

The author would like to regard his book as a tribute to the pioneers of sexhormone physiology, with special regard to John Hunter (1728-93), the first and greatest of them. More than a hundred years before the term hormone had been invented, Hunter showed that the accessory reproductive organs are largely dependent for their development and even for their existence on some influence derived from the gonads.

Embryonic gonads. Embryonic Mullerian and Wolffian systems.

The Embryonic Gonads

IN reviewing the actions of oestrogen in the living body we have first to consider the question: ‘Can oestrogen influence the sex of the embryo; can it reverse the genetic trend towards a male or female development of the gonads? ’ Experimental difficulties have prevented a study of the actions of oestrogen on the mammalian embryo in the earliest stages, and therefore the question proposed above must be left open as regards mammals. In amphibia and birds evidence of sex reversal has been brought forward, but even in these the reversal is incomplete (p. 184).

Burns (1925) joined in parabiosis larval salamanders (Amblystoma punctatum). Eighty such pairs survived until it was possible to identify the sexes by histology. In every instance the pairs were of the same sex, the twins were both male in forty-four instances and both female in thirty-six. No intersexual abnormalities were discovered, every pair consisting of perfect males or perfect females. Apparently in this experiment a reversal of sex must have occurred in approximately half the number of original individuals. The cause of sex reversal in this case cannot be stated; it may or may not have been due to gonadal hormones, but the experiment does seem to show that in these salamanders the genetic determination of sex is not necessarily final in every respect.

Ackart & Leavy (1939) experimented with larval axolotls (Amblystoma tigrinum). When the larvae were 30 mm. in length, at which stage sex differentiation was beginning, biweekly injections of 257 of oestrone were started and continued until the larvae had a length of 65 mm., the total dose of oestrone being 3507. At the end of this treatment there were no typical males,.nine of the fifteen survivors being normal females, the remaining six having gonads which resembled ovaries and on microscopical examination were found to be ovotestes. From this it appears that the genetically determined sexes of these larvae had not been changed by the treatment with oestrone, though the male gonads had been modified.

Foote (1940) performed the same sort of experiment, using larvae of two species (Amblystoma maculatum and A. tigrinum). Treatment of the former was started when the larvae were 57 days old and continued until metamorphosis occurred between the 110th and 142nd days.

Seasonal changes. The oestrous cycle. Pregnancy, pseudopregnancy and lactation. Gonadal hormones. Gonadotrophin. Sex. Castration, and destruction of seminal epithelium. Nutrition. Age.

SINCE Fichera (1905 a) called attention to the fact that castration is followed by enlargement of the anterior lobe of the pituitary gland with histological changes in its structure, many workers have confirmed and amplified his original observations ; and the cytology of the pituitary has become a subject of much importance in endocrinological studies of various kinds. The matter will be discussed briefly here in order to correlate, if possible, the changing cellular constitution of the pituitary with its gonadotrophic functions and with the activities of the reproductive organs.

Normally the glandular cells of the anterior lobe of the pituitary are of three main types, namely chromophobe, eosinophile and basophile, the chromophobe being regarded as the parent of the other two. The relative numbers of these cells vary in different physiological conditions. Besides this changing numerical relationship the cells undergo alterations in volume and other features during different stages of sexual activity. In pregnant or castrated animals, cells with special and distinctive characters occur and are known as ‘ pregnancy cells’ and ‘castration cells’ respectively. In the embryo chromophobes only are seen (Tuchmann, 1937).

Seasonal Changes

In animals with limited breeding seasons, during periods of sexual quiet when the output of gonadotrophin is at a minimum, small chromophobe cells predominate in the pituitary; a resumption of the sexual function is associated with an increase in the number and dimensions of the chromophiles. Cushing & Goetsch (1913, 1915) observed that sexual inactivity, whether associated with clinical evidence of hypopituitarism in man, or with experimentally produced pituitary deficiency in animals, or during hibernation, is accompanied by a reduction in the number and size of the chromophilic cells in the pars anterior. They confirmed the work of Gemelli (1906), who studied the seasonal changes in the pituitary of the marmot and showed that in this animal at the end of hibernation the pituitary swells, the glandular cells enlarge and the chromophiles stain more deeply.