HORMONES AND REPRODUCTION 49 



this hormone appears to be the induction of gonad 

 maturation in both sexes. 



The second gonadotropic hormone of the pituitary 

 does not induce this reaction. Its primary function is 

 seen most clearly in female mammals in which, after 

 ovulation, it stimulates the luteinization of the old follicle 

 cells to form the corpus luteum. For this reason it is 

 often known as the luteinizing hormone, or L.H, for 

 short. It is also said to stimulate the growth and function 

 of the non-germinal interstitial tissue in both ovaries 

 and testes, whence it is also known as the interstitial- 

 cell-stimulating-hormone, or I.C.S.H. for short. Its 

 action in the lower vertebrates remains uncertain, but 

 perhaps it functions in similar ways. 



When used together F.S.H. and I.C.S.H. reinforce 

 each other. Thus when F.S.H. is injected into 21 day 

 old rats, a given dose induces the ovaries to grow to a 

 weight of about 40 mg. while the same dose with added 

 I.C.S.H. causes grov^^th to about 80 mg.®^ Since I.C.S.H. 

 alone has no effect in these circumstances it is suggested 

 that it acts by sensitizing the gonad to the stimulation of 

 F.S.H. Similarly Lipschiitz^^? ^nd others have shown that 

 while F.S.H. does not itself affect the development of 

 corpora lutea, it greatly augments the luteinizing power 

 of I.C.S.H. Indeed it has been suggested that F.S.H. 

 is powerless to stimulate follicle growth in the mammal- 

 ian ovary unless some I.C.S.H. is also present, and 

 similarly that I.C.S.H. cannot cause luteinization in the 

 absence of F.S.H.^^ ^t this somewhat confusing point 

 the warning must bfe issued that the separate identities 

 of F.S.H. and I.C.S.H. in the normal pituitary secretion 

 have not yet been finally established. While it seems 

 probable that they are in fact distinct chemical com- 

 pounds, the suspicion remains that some yet unrecog- 

 nized circumstances in the method of preparation of the 

 extracts for experimental purposes may lead to different 

 responses by the gonads to one and the same hormone. ^^ 



The above observations relate almost exclusively to 



