INTRODUCTION 19 



immediate effects discussed in the preceding paragraph, has also an im- 

 portant relation to the developmental processes. This is obvious from a 

 comparison of a stunted cretin in whom the thyroid function is suppressed 

 with a normal subject of the same age. The anterior lobe of the hypoph- 

 ysis, the interstitial cells of the gonads, and the corpus luteum also have 

 important morphogenetic functions. 



Regarding the details as to how the morphogenetic functions are 

 mediated, we have little clean-cut information. Practically nothing is 

 known as to how deficiency of the hypophysis leads to disproportion of 

 development in the extremities, the skeleton, and the connective tissues; 

 or how the overdevelopment of acromegaly, which is due supposedly to 

 overactivity of the hypophysis, is brought about. That castration results 

 in a prolonged failure of the epiphyses of the bones to close is well known 

 but totally unexplained. We have little definite knowledge as to why 

 thyroid deficiency leads on the one hand to redundancy of subcutaneous 

 material, thus giving rise to myxedema, and on the other hand to arrested 

 development of the skeleton and particularly of the long bones. That 

 the endocrin factors in bone development act in quite different ways is 

 obvious. The hypertrophy seen in acromegaly gives a picture quite unlike 

 the increased growth in the length of bones of castrated subjects. 



Other important manifestations of harmozone influences may be seen 

 in the development of the genital tract and its accessory glands. In the 

 male a condition of genital infantilism can be brought about through 

 aplasia of the interstitial cells, the so-called "puberal gland" of the 

 testes, as well as, according to many investigators, perturbed functions of 

 the hypophysis or the pineal gland. Similarly, thyroid deficiency may 

 result in defective development of the genitalia. In the female, normal 

 development of the internal genitalia and of the breasts may be prevented 

 either by thyroid or ovarian deficiency. That various changes in the 

 uterus during the menstrual cycle and numerous bodily changes in preg- 

 nancy are due to the corpus luteum or to the interstitial cells of the ovary 

 is highly probable. Ochoterena and Remirez have discussed the evidence 

 on this point. 



That some of the morphogenetic factors discussed in the foregoing 

 paragraph may exert their influence through the nervous system is 

 possible. That such changes as mammary hyperplasia, however, can 

 readily be demonstrated after denervation of the gland indicates that in 

 some cases, at any rate, trie influence is directly upon the tissue cells. 



Regarding the problems of the mediation of, hormone control only a 

 beginning has been made. The future will doubtless see developments of 

 the highest importance both to general biology and to clinical medicine. 

 Further data along this line will be found in subsequent chapters on "The 

 Relation of the Endocrin Organs to Growth and Development" and "The 

 Relation of Endocrin Organs to Metabolism." 



