96 INTERNAL SECRETIONS 



gradually in from three to four days. The reflex could be 

 evoked again when new injections were made. Such striking 

 results were not, indeed, obtained in all the experiments 

 performed, but in the greater number the reflex could be 

 evoked after injection. The disappearance of the clasp reflex 

 evoked by injections could be accelerated by washing out the 

 dorsal lymph sac with isotonic salt solution. According to 

 Steinach, among frogs caught at the time of heat some are 

 found in which the clasp reflex is naturally absent; in these 

 animals also, however, the reflex could be evoked after injection. 

 Control experiments were made with pulp of muscle and hver of 

 frogs in heat, but no effect could be obtained. Simultaneously 

 with Steinach' s work a paper was published by Harms (1910) 

 containing an account of similar observations on the clasp 

 reflex. The above-mentioned observations of Nussbaum on the 

 influence produced by testicular injections on the thumb pads 

 were confirmed by Steinach, Harms, Mcisenheimer (1912), and 

 Takahashi (1919). 



All these experiments performed on mammals, birds and 

 amphibians show that the formative and preserving effects 

 possessed by the sexual glands in relation to the sex characters 

 are caused not by nervous impulses from these glands, but by 

 chemical substances secreted by the latter into the circulation. 

 We know practically nothing about the chemical nature of these 

 substances. But they are in any case specific, as the same 

 effect cannot be evoked by the injection of any other gland or 

 tissue. The active substances present in the sexual gland are 

 therefore specific hormones. The question as to the chemical 

 nature of these hormones will be discussed more fully in 

 Chapter VII. 



According to Steinach the clasp reflex can be evoked only 

 by testicular injection from a frog in heat. When heat is over, 

 the testicle has no effect when injected into a " castrate." 

 From this one would conclude that the specific hormone 

 evoking the clasp reflex is produced only at the time of heat. 



