72 INTERNAL SECRETION 



limb, associated with an increased muscular development 

 in the forearm. This modification is preparatory to the act of 

 copulation, when the male frog uses its arms in embracing the 

 female, and so assists in pressing out the eggs from the oviduct. 

 If the male frog be castrated, the pad is not formed, and the 

 muscles do not develop. Nussbaum found that when pieces of 

 testis were introduced into the dorsal lymph sac of a castrated 

 frog, the swelling on the thumb and hypertrophy of the muscles 

 of the leg took place just as though the frog had not been 

 castrated. This development of a secondary sexual 

 characteristic must have been due to the absorption of sub- 

 stances (internal secretions) derived from the testicular tissue, 

 since there was no nervous connection. If, however, the nerves 

 supplying the muscle of the forearm were severed (in an entire 

 frog) the enlargement did not occur. A similar result was 

 brought about on transsecting the nerve supplying the glands 

 and papillae of the thumb -swelling. Nussbaum concludes, 

 therefore, that the internal secretion provided by the testis acts 

 through the medium of the nerves. It has, however, been 

 pointed out that in similar cases it has been shown that the 

 apparent effect of the transsection of nerves is due to the loss 

 of sensibility in the parts concerned, in consequence of which 

 the tissues are not guarded from injury. 



Transplantation of the testis was carried out by Hunter and 

 by Berthold, and, apparently, with complete success. In cocks 

 Berthold found that the secondary sexual characters were 

 retained after transplantation, and the author puts forward 

 what is practically the modern view of internal secretion, 

 except that he considers the nervous system to play an impor- 

 tant part. 



A subject of peculiar interest is the influence of the testis 

 upon growth in general, and upon the growth of bone in parti- 

 cular. There has long been a belief in a definite antagonism 

 between growth and sexual activity. It was laid down as a 

 general biological principle by Carpenter, Spencer, and others, 

 that the functions of nutrition and reproduction are essentially 

 opposed to one another, because reproduction makes such a 

 demand upon the parent for material that the supply for 

 nutrition and growth of the parent is lessened. This philoso- 

 phical generalization has been vigorously combated by Mi not, 

 Morgan, and others. However this may be, abundant evidence 



