52 BIOLOGY AND SOCIAL PROBLEMS 



such a production of adrenalin that the con- 

 ditions already described are almost immedi- 

 ately present ; in other words, when an animal 

 is excited to fear or rage or subjected to phys- 

 ical pain, its whole neuromuscular mechanism 

 and related parts are thrown into a condition 

 most favorable for vigorous and protracted 

 response. The biological significance of this 

 set of relations from the standpoint of the 

 struggle for existence must be clearly evident, 

 and we see again how a highly complex sys- 

 tem of organic interrelations can be developed 

 on a principle other than that of nervous 

 control. 



Just as the thyroid and the adrenals can 

 exert a profound influence on the activities of 

 the body through their hormones, so the sex- 

 ual glands can effect changes in a like manner 

 and quite independently of their usual prod- 

 ucts. This subject has been worked upon 

 recently with very interesting results by Stein- 

 ach. The method employed by this investi- 

 gator was as follows : Young male rats and 

 guinea-pigs were first castrated, after which 

 the ovaries from a young female of the appro- 

 priate species were grafted under the abdom- 

 inal skin of each castrated male. The animals 



