886 PHYSIOLOGY OF DIGESTION AND SECRETION. 



Steinach states that such an animal is sought by the male as 

 though it were a true female. It would follow from these experi- 

 ments that the internal secretion of the interstitial cells in the ovary 

 and in the testis has each its specific influence in guiding the de- 

 velopment of the sexual characteristics, one causing the formation 

 of male, the other of female characteristics. Many experiments 

 and observations indicate that the internal secretions of the ovaries 

 and testes are important, not only as regards so-called secondary 

 sexual characteristics, but also in regard to the body-metabolisms in 

 general. Some evidence for this general view is found in the 

 functional relationship that appears to exist between these organs 

 and other ductless glands. This relationship is most clearly 

 marked with the thymus, the pituitary, and the cortical portion of 

 the adrenal glands. Castration or spaying causes an enlargement 

 of the thymus gland, even in the mature animal in which this gland 

 has undergone considerable involution. The same operation 

 affects the hypophysis and adrenals, although, according to Hatai,* 

 the effect in this case varies with the sex. In the male castration 

 causes a marked increase in the weight of the hypophysis, while in 

 the female the effect is less distinct. As regards the adrenal glands, 

 castration in the male causes an increased weight of the adrenals, 

 while spaying in the female causes a decrease in weight in these 

 glands. On the other hand, as has been stated above, thymectomy 

 seems to accelerate the development of the reproductive glands, 

 and removal of the posterior lobe of the hypophysis retards their 

 development. The nature of these reciprocal relationships can- 

 not be explained at present, but it may be assumed that they are 

 concerned with modifications of the nature of some of the processes 

 of body-metabolism and that the effects produced depend upon 

 definite hormones or internal secretions. Further evidence of the 

 same character may be found in observations like the following: 

 In gynecological practice it has been observed that complete 

 ovariotomy with its resulting premature menopause is often 

 followed by distressing symptoms, mental and physical. In 

 such cases many observers have reported that these symptoms 

 may be alleviated by the use of ovarian extracts. Similar results 

 have been reported upon the lower animals. After complete ovari- 

 otomy a condition of "heat" may be reproduced by grafting ovarian 

 tissue, f and several observers agree in stating that removal of the 

 ovaries in young animals prevents the normal development of the 

 uterus, while in adult animals it causes the organ to undergo a 

 fibrous degeneration (see section on Reproduction). In the 

 natural menopause, as well as in the premature menopause follow- 



* Hatai, "The Journal of Experimental Zoology," 18, 1, 1915. 



t Marshall and Jolly, "Philosophical Transactions," B. cxcvii., 99, 1905. 



