THE NATURE OF LIFE 



the blood stream as the result of anger, 

 thereby increasing the muscular tonus. 

 It affects also the nervous system and 

 other organs. 



The fact that the injection or feeding 

 of hormones has such marked effects 

 leads us to ask whether other substances 

 can be used in the same way. As a mat- 

 ter of fact a great variety of substances 

 can be used to influence development. 

 We may mention the fact that when 

 plant lice are placed upon rose twigs 

 whose lower ends dip into water the de- 

 velopment of the insect may be easily 

 determined by substances added to the 

 water. Thus a variety of salts can be 

 added to the water which insure that 

 the plant lice acquire wings; but if alco- 

 hol is added to the water they remain 

 wingless. 



Stockard, and later McClendon, found 

 that by adding alcohol and other sub- 

 stances to the sea water the developing 

 fish produced cyclopean eyes, that is, the 

 two eyes were fused into one. 



