200 E. UHLENHUTH 



There are two, as yet incompletely studied, phenomena which seem 

 to contradict the conception of the hormonic development of the secondary 

 sex characters; these are the occurrence of gynandromorphs in birds 

 (Weber), in which one-half of the body is completely male, the other 

 completely female, and Morpurgo's parabiotic rats. An incomplete knowl- 

 edge of the conditions existing in these cases and a lack of space forbid 

 discussion of their significance. 



Little is known as to the mechanism of the action of the sex hormones, 

 beyond the fact that they cause increased metabolism (Loewy and 

 Kichter). This agrees perhaps with Steinach's recent discoveries that 

 the morphogenic effect of the sex hormones is quantitative ; a mere hyper- 

 plasia of the interstitial gland of the ovary grafted into the castrated 

 male leads to development beyond the female virgin characters and 

 produces the structures characteristic of pregnant females. 



Finally, it should be mentioned that removal of the sex glands results 

 in overgrowth of the long bones. It is, however, doubtful whether or 

 not the sex hormones possess a specific inhibitory action on growth. Facts 

 are known which indicate hyperfunction of the pituitary gland after 

 castration, especially in the male (see Hatai and under hypophysis). 

 This finding in connection with the fact that castration delays closure of 

 the epiphyses (Sellheim, Tandler and Grosz) may account for the over- 

 growth of castrated individuals. 



Relations of the Thymus to Growth and Development 



After Basch in 1903 had published his first accounts of a new method 

 which permitted complete removal of the thymus gland from mammals, 

 the view became widespread that the thymus plays an important role 

 in growth and development. The numerous and elaborate publications 

 by Basch, Kloso and Klose's collaborators are responsible for this view. 

 According to the experiments of these investigators, performed mostly 

 on dogs, the following conditions may be observed, when the thymus is 

 extirpated from dogs and other mammals a few weeks after birth. First, 

 the growth of the animal as a whole is retarded ; second, specific disturb- 

 ances of the development of the skeleton result; third, development of 

 the mental abilities is disturbed; fourth, hypertrophy of the sex glands 

 is caused. Since TClose had found that these conditions develop only if 

 the thymus is extirpated in very young animals, his results apparently 

 received much support from the opinion that the thymus gland functions 

 only during early postfetal development and atrophies after sexual 

 maturity is reached, irammar, however, has shown that this opinion is 

 not correct; careful measurements of the thymus gland of healthy indi- 

 viduals of different ages demonstrated that the thymus gland persists after 



