GROWTH AND CHEMICAL PURITY 277 



brain has been driven to overwork by the requirements 

 of pregnancy. 



Adrenals: It is known that the adrenals enlarge 

 in animals in advance of their mating season and that 

 the enlargement persists during pregnancy. Such 



FIG. 69. TRACING SHOWING EFFECT OF PREGNANCY ON THE ADRENAL 

 OUTPUT OF A CAT. (Cannon Test.) 



That the adrenal glands are activated during pregnancy is demonstrated 

 by the sharp inhibition of the contractions of intestinal muscle when the 

 blood of a pregnant cat is substituted for normal blood. 



seasonal enlargement and its persistence during preg- 

 nancy indicate an adaptation to the work of pregnancy 

 a preparation on the part of the adrenals for a useful 

 participation in pregnancy. In addition to this ana- 

 tomical evidence, we found an increase of adrenin in 

 the blood of a pregnant rabbit. (Fig. 69.) Further- 



