Influence of STH and Cortisone on Foetal Growth 165 



growth of the rat but inhibits it and makes it possible to 

 obtain embryos of younger appearance than the normal 

 embryos of that age. 



These observations led us to examine two other aspects of 

 this problem : the possible mechanism of the action of STH 

 and the part played by the maternal pituitary in embryonic 

 development. The causes of the inhibition of embryonic 

 development observed with STH are difficult to explain. We 



l.S 



1 



Controls 



S. T. H. 



i 



!> k S 6 7 



Day treatment commenced 



Fig. 0. Average weight of embryos removed on the 20th day of 



gestation; the differences in weight are only significant when 



STH is administered before the 5th day of gestation. 



were tempted to explain it by an increase of maternal protein 

 anabolism. This could in fact deprive the foetus of part of the 

 nutritive substances intended for it. However, a comple- 

 mentary experiment, in which we commenced STH adminis- 

 tration 4, 5, 6, 7 and 8 days after conception, showed us that 

 foetal growth is inhibited to a significant degree only when 

 STH is administered before the 5th day of gestation (Fig. 6). 

 This fact suggests another mechanism, for example an early 

 enzymatic disturbance, which has a deleterious effect on the 

 development of the embryo, as has been clearly shown by the 

 work of Warkany (1948) and Giroud (1954). 



