80 PHYSIOLOGY CHAP. 



other hand, mere dilatation of the vesicle with an indifferent fluid, 

 such as milk, creates the sexual impulse artificially. 



Accordingly, in spawning, when the nerve-centres are highly 

 excitable, the impulse that gives rise to sexual desire conies from 

 the dilatation of the seminal vesicles, and is transmitted by the 

 sensory roots. This is the fundamental factor that gives rise in 

 the male to the desire to seek the female and to copulate with 

 her. During copulation, the whole of the senses with their 

 respective nerve-centres are active, and it is necessary to extirpate 

 them all before the clasp can be inhibited. 



No doubt much the same process takes place in the higher 

 animals. Every one knows that in mammals, e.g. in dogs, the 

 odour guides the male to find the female, and increases the 

 erection of the genital organs due to repletion of the spermatic 

 vesicles ; it is more particularly the odour of the secretion from 

 the small glands of the mucous membrane of the vulva of the 

 female that exerts powerful attraction on the male. The other 

 senses are, however, actively involved in different degrees. 



As regards the special centres connected in mammals and in 

 man with sexual desire, the cerebellum according to the theory 

 of Gall, revived by Lussana and of late years by Bunge is the 



tntre of the reproductive instinct, of physical love or the erotic 

 nse. This theory was effectively put out of court by our experi- 

 ments on the total extirpation of the cerebellum in dogs. After 

 this operation dogs have, like normal animals, their periods of 

 sexual excitement and all the concomitant erotic phenomena : 

 bitches have periods of heat, in which the whole mucous mem- 

 brane of the genital organs is congested and secretes a viscid, 

 bloody fluid which excites the olfactory sense in the male, whose 

 advances are received with evident pleasure by the female two, 

 three, or even more suitors being accepted. 



On the other hand, Goltz' researches on the effect of successive 

 ablations of the hemispheres proved that sexual desire is 

 diminished with each successive mutilation. But he notes 

 expressly that dogs with a small residue of cerebral cortex still 

 exhibit traces of sexual impulse, since they sniff at the genital 

 organs of other dogs, even if only momentarily. The " brainless 

 dog," on the contrary, never gave the slightest sign of sexual 

 attraction during the eighteen months in which it was under 

 observation. So that there can be no doubt that the centre 

 which is particularly active before and during coitus lies in the 

 fore-brain. But in which portion of it ? If it were credible, as 

 some state, that excision of the olfactory lobes and nerves 

 obliterates the sexual impulse in dogs, the question would be 

 solved ; but as we have not controlled this assertion we cannot 

 accept it unreservedly. 



Broadly speaking, the same facts can be observed in man as 



