78 PHYSIOLOGY CHAP. 



causes of the excitation which, it' transmitted to ihr centres, 

 produces the consensus of pleasant and voluptuous sensations 

 that finally lead to completion of the sexual act. 



The sex impulse is essentially connected with the presence of 

 the male and female germinal elements, the spermato/oon and the 

 ovule. This is the fundamental fact by which the indispensable 

 internal conditions of sexual impulses are determined. Evidence 

 for this is afforded by castration, which as a rule abolishes or 

 checks sexual desire. To this rule there are undeniable excep- 

 tions: the Mussulmans accordingly insist that the guardians of 

 their harems shall undergo amputation of the penis as well as 

 the testicles. The exceptional occurrence of erotic erection in 

 castrated persons is probably due to the castration having been 

 performed not in infancy but in advanced childhood or adolescence. 



Another interesting fact may be observed in eunuchs. Alt hough 

 they lose the reproductive desire properly so-called, the voluptuous 

 sensations of sexual affection are not wholly abolished, viz. such as 

 are furnished by sight, hearing, the tactile and muscular sense, 

 and the olfactory sense. Owing to these impulses they become 

 enamoured of their charges, and are the more strict as gaolers in 

 proportion as their passions are involved. 



We have thus sutlicient evidence that the internal conditions 

 of the erotic excitation which arouses sex desire consist in the 

 development and accumulation of the germinal elements in both 

 sexes, but that the internal excitation is constantly associated with 

 external stimulation from the peripheral organs of the special 

 senses, which may persist even after castration. 



Animals exhibit practically the same phenomena. Experi- 

 ments have been made un them to determine the relative import- 

 ance of the respective senses in regard to sexual desire, and the 

 results are to a large extent applicable to man also. 



In the first place there is the work of Lazzaro Spallanzani, 

 who made a great number of experiments on reproduction, 

 particularly on toads and frogs. He observed that during copula- 

 tion these animals may be pricked, wounded, and mutilated in 

 various ways without loosening the sexual clasp. The following 

 experiment is particularly interesting: 1 "Finding two toads in 

 copulation I separated them forcibly ; I cut off the thighs of the 

 male and put it down near the female ; it then embraced her 

 anew. I cut off the hands of a male toad and placed it near a 

 female ; as we know, the males use their hands in copulation ; it 

 seized the female with its bleeding stumps and did not release 

 her till all the ova were fertilised. On cutting off the head of a 

 male frog in the act of copulation, it did not let go of the female 

 with its arms and hands ; it bathed the ova for an hour and 

 three quarters with its seminal fluid, and nearly all of them 

 1 Quoted from the Genevan edition of 1876, by Senebier. 



