212 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



testicular extracts cannot be estimated at present, in spite of the large litera- 

 ture upon the subject ; we must wait for more detailed and exact experiments, 

 which doubtless will soon be made. Quite recently Zoth l and also Pregel 2 

 seem to have obtained exact objective proof, by means of ergographic records, 

 of the stimulating action of the testicular extracts upon the neuro-muscular 

 apparatus in man. They find that injections of the testicular extracts cause not 

 only a diminution in the muscular and nervous fatigue resulting from muscu- 

 lar work, but also lessen the subjective fatigue sensations. The fact that the 

 internal secretion of the testis, if it exists at all, is not absolutely essential to 

 the life of the body as a whole, as in the case of the thyroids, adrenals, and 

 pancreas, naturally makes the satisfactory determination of its existence and 

 action a more difficult task. 



1 Pftuger's Archivfiir die gesammle Physiologic, 1896, Bd. 62, S. 335. 2 Ibid., S. 379. 



