APPENDIX II 



substances that stimulate the growth and differentiation of 

 the ovaries and testes of animals into which they are in- 

 jected. The precise nature of the effects of these hormones 

 differs considerably, however, according to the particular 

 source of the hormone and also according to the species of 

 animal receiving the injections and the dosage. Under these 

 varying circumstances, the constituent tissues of the ovary, 

 for example, respond differently. Sometimes the follicles 

 merely grow larger or even become cystic or atretic ; in other 

 experiments they are caused to form corpora lutea. In the 

 testis likewise, there may be stimulation on one hand of the 

 spermatogenic tubules, on the other hand of the interstitial 

 cells (see Chapter IX). Workers using the ovaries of various 

 species as test objects have found first that as their efforts 

 to purify the gonadotrophic substances advanced, they 

 seemed more and more clearly able to achieve at least partial 

 separation of the two effects just mentioned; that is to say 

 some of the partially purified preparations tended to pro- 

 duce only follicle stimulation, others only to cause luteiniza- 

 tion. Separation of the two effects, perhaps even better than 

 can be attained as yet in the chemist's flasks, is observed as a 

 result of biological processes. To mention one example, urine 

 of women after the menopause, or after removal of the 

 ovaries, contains a substance presumably produced by the 

 pituitary gland that has almost pure follicle-stimulating 

 properties. The hypothesis has therefore sprung up that the 

 pituitary gland produces two distinct hormones, usually 

 denoted respectively by the initial letters FSH for "follicle- 

 stimulating hormone," and LH for "luteinizing hormone." 

 There is ample evidence that the gonadotrophic substances 

 are of protein nature, and this is sufficient explanation of the 

 fact that as yet, in spite of immense effort, no one has ob- 

 tained preparations which solely give one or the other effect 

 upon test-animals. The question therefore remains unsettled 

 whether there are two hormones, chemically separable, or one 



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