694 A MANUAL OF VETERINARY PHYSIOLOGY 



proliferation. This periodic development of the accessory genera- 

 tive organs in the hedgehog is regarded by Marshall as due to an 

 internal secretion of the testicle. 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 Period of Puberty, or that time in the animal's life when 

 it is capable of procreation, has been put at one and a half years 

 for the horse, eight to twelve months for bo vines, and six to 

 eight months for the sheep, pig, and dog. There is, however, 

 a great difference between capability and fitness for procreation. 

 Breeding from immature animals is one explanation of a great 

 deal of the worthless material in the shape of horses which may 

 be seen in all countries. The horse is commonly believed to be 

 mature at five years of age ; he ought not to be regarded as 

 mature until he has attained his sixth year. Bracy Clark even 

 thought about the eighth year. The ass, according to Crisp, is 

 mature at five years ; the ox, sheep, and goat at four ; the pig 

 at three. The elephant is generally considered mature at fifty, 

 but Crisp says he does not cut his last tooth until eighty years 

 of age. 



The advent of maturity is marked by certain changes in form, 

 particularly in horses. They lose their awkwardness, the out- 

 line of the frame becomes more consolidated and in greater 

 unison. In the male the neck becomes thick and curved, the 

 voice deepens, and the whole appearance denotes life and vigour. 

 In both the stallion and bull the temper is usually irritable and 

 uncertain, and often extremely vicious. The age at which pro- 

 creation ceases is not known. Mares have produced foals at 

 twenty-eight, thirty-two, and thirty-eight years of age,* and it 

 is certain that some good stallions have been advanced in years. 



The Act of Erection is a vascular phenomenon produced by 

 an engorgement of the erectile tissue of the penis with blood. 

 This engorgement is brought about by stimulation of the nervi 

 erigentes, which are derived from the autonomic system, and 

 arise from the sacral portion of the cord. These nerves furnish 

 dilator fibres to the vessels of the penis, and under their influence 

 the cavernous spaces of the erectile tissue become gorged with 

 blood under pressure. The nervi erigentes act reflexly through 

 an erection centre in the cord, while the erection centre is under 



* In a paper on ' The Growth and Maturity of Animals,' by Dr. E. Crisp, 

 referred to above, the writer states he knew a Suffolk cart-mare that bred 

 a foal at the age of thirty-nine (Veterinary Review and Stockowners' 

 Journal, March, 1865). 



The ' Tartar Mare ' was considered to be thirty-four to thirty-six years 

 of age when she bred 'Queen Mab.' 'Driver,' an Australian imported 

 mare, bred ' Moss Rose ' at thirty-three (Standard, December 25, 1893). 



