262 THE PHYSIOLOGY OF REPRODUCTION 



cord. As already mentioned, Brachet observed ejaculation 

 after all connection with the higher centres had been cut off. 

 The centripetal nerves for the ejaculatory reflex are the sensory 

 nerves of the penis, the stimulation of the glans being particu- 

 larly effective. 1 



Erection has been observed to occur in animals which were 

 castrated late in life, sexual desire in such cases being to some 

 extent retained. It has been shown, however, that erection 

 cannot be induced experimentally in animals which have been 

 castrated prior to puberty ; or, at any rate, that it is far more 

 difficult to cause erection in such animals. Thus, in three 

 experiments carried out by the writer, in conjunction with 

 Professor Sutherland Simpson, 2 it was found impossible to induce 

 erection by stimulating the nervi erigentes in three cats which 

 were castrated when about half grown and afterwards allowed 

 to reach their full size. It is possible, therefore, that in such 

 animals the muscular apparatus of the penis fails to develop 

 sufficiently to admit of erection occurring, but it would seem 

 unlikely that the nervous mechanism is impaired. If erection 

 is due mainly to an inhibition of the vaso-motors of the penis, 

 as is ordinarily supposed, there would seem to be no theoretical 

 reason why it should not be possible to bring about that process 

 experimentally in castrated animals. It is conceivable, there- 

 fore, that the process of erection is after all a more complex 

 phenomenon than is generally believed, but our experiments 

 throw no further light on the mechanism of that process. 



1 For further references to the literature of the nervous mechanism of 

 erection and ejaculation, see Bechterew, Die Funktionen der Nervencentra, 

 Weinberg's German Translation, vol. i., Jena, 1908. 



2 Simpson and Marshall, " On the Effect of Stimulating the Nervi 

 Erigentes in Castrated Animals," Quar. Jour. Exper. Phya., vol. i., 1908. 



