26 Alfred Jost 



such as the liver, also pass through a physiological turning- 

 point, but the importance of this change for later postnatal 

 life is not yet established. 



The study of the pituitary gland in the rabbit or of the 

 testicular interstitial cells in man, for instance, strongly 

 suggests that such endocrine glands could pass through a 

 period of maximal working at certain prenatal stages, fol- 

 lowed by a period of lesser activity. It would then appear that 

 the normal development of the foetus involves distinct endo- 

 crine events at appropriate stages. 



Finally, although only one example of an actually transient 

 tissue was considered in this paper, namely the Wolffian 

 duct, the points which were discussed cannot be considered as 

 too far from the main object of this colloquium, if the idea will 

 be accepted that the term " foetus " does not define a particular 

 state of an animal but covers a succession of different transient 

 stages leading up to each other. 



Acknowledgement. 



We are indebted and wish to extend our thanks to several Labora- 

 tories which kindly supplied the homones used in these researches: 

 Dr. Choay (Choay Laboratory) for growth hormone and insulin; Dr. 

 Tausk (Organon, Holland) for ACTH; Dr. Velluz (Roussel— UCLAF), 

 for cortisone, hydrocortisone, desoxycorticosterone acetate; Dr. Borman 

 (Squibb) for 9-a-fluorohydrocortisone. 



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