•S7<S .1 Manual of Veterinary Physiology. 



of the female. The vitality of the spermatozoa is consider- 

 able under suitable conditions ; and when placed in the 

 body of the opposite sex they have been found vary active 

 seven or eight days after copulation. Colin has found 

 them in a similar state in the vesicuhe seminales eight 

 days after castration. The spermatozoa are readily killed. 

 Colin says that those of the ox, horse, and carnivore 

 are killed immediately by ordinary or acidulated water, 

 glycerine, etc. 



The prostatic fluid precedes the spermatic in ejaculation, 

 and in stallions and bulls, when excessive daily demands 

 are made, the fluid ejaculated is largely prostatic and 

 infertile. 



The testicular products of hybrids, such as the mule, are 

 said to be devoid of spermatozoa. 



The act of copulation consists in the introduction of the 

 penis of the male into the vagina of the female. With 

 some animals, as in the dog, the introduction is facilitated 

 by the presence of a bone in the substance of the penis ; 

 but in all animals the penis has to become erect and larger 

 before it is fit for penetration. 



The Phenomena of Erection is produced by a gorging of 

 the vessels of the penis, caused by a dilatation of the 

 arteries, increased blood supply, and pressure on the veins. 

 This is brought about by the nervi erigentes, the fibres 

 of which contain both dilator and constrictor nerves for 

 the walls of the bloodvessels. An erection centre also 

 exists in the spinal cord, normally under the control of the 

 vaso-motor centre in the medulla, though it may act inde- 

 pendently of it, as in persistent erection after laceration of 

 the cord. The stimulation of the centre in the medulla 

 may even at the moment of death lead to erection and 

 ejaculation. Colin has observed this in stallions destroyed 

 by section of the medulla, injuries to the head, or even simply 

 by bleeding. The emptying of the bladder and evacuation 

 of the contents of the intestines, in horses destroyed by 

 shooting through the head, is a regular accompaniment of 

 this mode of death, and the same prooe8S which empties 



