82 MULES AND MULE BRFJEBING. 



tlie ass appear to be ordinary mules, and are sterile, whereas 

 if she were a mule they should be three-fourths asinine and 

 only one-fourth equine, which is not the case. Her progeny 

 by the horse are horses which have proved fertile. It 

 would appear most probable that this is not a case of a 

 fertile mule breeding ; but, that the animal is really an 

 ordinary mare, whose female parent was influenced by a first 

 alliance, as is so often the case in dogs and other animals. 



There is no doubt that the majority of the accounts of 

 supposed fertile mules owe their origin to the fact that 

 abnormal lactation not unfrequently occurs in them, when 

 milk is secreted in great abundance, and they may be seen 

 suckling the foals of other animals. This singular 

 phenomenon is not confined to mules, but is well known to 

 occur in many other species. 



The maternal instinct is one of the most powerful, and 

 there are numerous examples of its beiug so strongly 

 excited in females (other than the mother) in favour of the 

 young of animals of the same, and even of different species, 

 as to determine the abundant secretion of milk. Domestic 

 animals, such as cats and dogs, have been known to suckle 

 young of other species, even when they had no progeny of 

 their own; and corresponding instances among women who 

 have fostered orphan children are on record in the 

 physiological journals. Nay, more than this, a case is 

 related by Humboldt of a man who became the wet nurse 

 to an infant child. " In the village of Arenas there lived 

 a labourer, Francisco Lozano, who had suckled a child. 

 Its mother happening to be sick, he took it, and, in order 

 to quiet it, pressed it to his breast, when the stimulus 

 imparted by the sucking of the child caused a flow of milk. 

 The man was examined by M. Bonpland, who found the 

 breasts wrinkled, like those of women who have nursed. 



