REGULATION OF GROWTH 



crude extracts than toward more purified extracts. It is diffi- 

 cult to correlate these observations with the conception of 

 "antihormones." 



Evans and his colleagues found that if hypophysectomized 

 rats failed to respond to an extract, there might occur a strik- 

 ing response if glucose solution was also administered paren- 

 terally.^ 



Factors influencing the assay of growth-promoting hor- 

 mone have been studied in normal and hypophysectomized 

 rats by Chow, Chang, Chen, and van Dyke (1938). In nor- 

 mal rats, in confirmation of the work of others, they found the 

 young adult female rat most suitable. Sex does not affect 

 the response of hypophysectomized rats which, in terms of 

 the percentage change in weight, is at least twice as great as 

 that of normal rats. Rats with a hypophysial deficiency of 

 8-10 months are less sensitive than those hypophysectomized 

 1-6 months before assay. Differences in response in relation 

 to dosage are more easily recognized in hypophysectomized 

 rats, whereas in normal rats a doubling of the dose may not 

 be followed by a change in response which is convincingly 

 greater. In either normal or hypophysectomized rats the 

 optimum period of injection probably is not longer than 10 

 days. Even 6 weeks after the use of rats for assay, their re- 

 sponse to a second course of injections is reduced. 



The preparation and purity of growth-pro?noting extracts of 

 the anterior pituitary. — The only recent attempts to purify 

 growth-promoting extracts are those of Dingemanse and 

 Freud (1935). They stated that their preparation contained 

 neither lactogenic nor thyrotropic hormone and that 0.025 

 mg. administered intraperitoneally once daily to hypophy- 

 sectomized rats (120-80 gm.) caused an average gain of 

 weight amounting to 7 gm. following administration for one 

 week. The method they described required the following 



'According to Shelton, Cavanaugh, and Long (1935), the effect of growth-pro- 

 moting extract in adult female rats is potentiated by the injection of 0.5 cc. of hu- 

 man serum 3-6 weeks previously. 



[45] 



