ISOLATION OF SEXUAL HORMONES 321 



why we must be very careful in drawing conclusions about such 

 experiments. The impression one gets when reading of- the 

 contradictory results obtained by different authors with 

 extracts of testes, ovaries, placenta and foetus is not a favour- 

 able one (see especially Gley, 1914, p. 42). Further, such 

 experiments are of a scientific value only when simultaneously 

 controlled- by experiments made with extracts from other 

 organs prepared in just the same manner without any technical 

 deviation. But even in this case the value of injection experi- 

 ments must remain a very limited one, because these experi- 

 ments are liable to give a very erroneous idea of the effects of 

 the sexual hormones produced by the gonads in the organism. 

 It is most likely that the extract contains only some of the 

 substances which normally are secreted by the sex glands; 

 most probably the manifold effects produced are due to 

 different hormones being secreted. There is little justification 

 for supposing that there is one male and one female sexual 

 hormone; as little justification as there would be in supposing 

 that adrenaline is the only hormone secreted by the adrenals. 

 Further, we have already mentioned the possibility that by 

 introducing extracts into the body, substances are introduced 

 which normally are never secreted by the sex glands. It must 

 also be taken into consideration that it is not possible to 

 imitate by injection the real quantitative and time relations of 

 the normal glandular function, to imitate, so to speak, the 

 rhythm of the normal function. There can be no doubt that 

 the normal functional rhythm of an endocrine gland is of the 

 greatest importance to the organism, and we must suppose 

 that the effects of the substances by which one organ acts on 

 another are subject to the general laws of stimulation. Quanti- 

 tative and time relations in internal secretion have so far been 

 very insufficiently studied on an experimental basis. But we 

 have seen in the foregoing chapters to how great an extent 

 quantitative problems are involved in investigating the 

 internal secretion of the sex glands. The experiments of 

 Pezard, as well -as our own, made on more or less quantitative 

 Unes, showed from the beginning that we are here on an almost 

 wholly unexplored terrain, where many special problems await 

 to be investigated. 



