98 INTERNAL SECRETIONS 



by which, possibly through local changes of blood supply, the 

 development of certain sex characters during the state of heat 

 would be promoted. But Pfluger (1907) raised the objection 

 that by sectioning the nerve of the forearm disturbances may 

 be caused which are sufficient to explain the underdevelop- 

 ment or degeneration of the pad. 



The question as to the role played by the nervous system 

 in regard to the effect of the sex glands on the somatic sexual 

 characters is a very important one. It would be useful to 

 investigate this question more fully than has so far been done 

 experimentally. 



2. Physiology of the Clasp Reflex. 



The clasp reflex is a relatively simple and very pronounced 

 physiological phenomenon characteristic of heat, and it may 

 be conveniently considered here in preference to the more com- 

 plicated psycho-sexual reactions observable in mammals. There 

 are no special difficulties in experimenting on the physiology of 

 the clasp reflex, whereas enormous difficulties arise when the 

 psycho-sexual reflexes of mammals and man are studied. 

 On the other hand the slight results obtained by experimental 

 investigation of the clasp reflex of the frog may show us that we 

 must not expect too much from research work on the psycho- 

 sexual reactions in mammals and man. We see that the question 

 as to the physiology of the clasp reflex, and the role played by 

 the internal secretion of the sex gland in connection with it, 

 is of a greater importance than one might at first think. 



The clasp reflex has been studied by many investigators and 

 over a long period. Spallanzani (1786, pp. 93 and 319) showed 

 experimentally that for the reflex to occur, only the spinal 

 cord and no higher parts are necessary. He decapitated male 

 frogs when clasping the females, and they continued to clasp. 

 We shall see below that by decapitation the clasp reflex can 

 be evoked even outside of the time of heat. Further detailed 

 experiments on the clasp reflex were made by Goltz (1869, 

 quoted from Tarchanoff, 1887), who stated that the clasp 

 reflex can be evoked when the skin of the breast or the ventral 

 side of the arm is stimulated. After excising these parts of the 

 skin or cutting through the corresponding posterior roots of 

 the spinal cord the clasp reflex can no longer be evoked. 

 According to Goltz there are influences emanating from the 



