316 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



VI. HUMINATION. 



In most animals the food after being swallowed enters the stomach 

 sufficiently comminuted to be at once acted on by the gastric juice. In 

 others, though imperfectly triturated, the food may be at once digested, 

 while in a third case the food is returned to the mouth for a second 

 mastication. 



The first of these cases is seen in carnivora and omnivora ; the 

 second occurs in granivorous birds and crustaceans, where mastication 

 in the mouth is entirely absent, but where, as will be seen later, the 

 stomach is provided with an accessory organ, the gizzard, which is 

 capable of crushing and grinding the food. 



The third case is seen in ruminants, where the food is carried to the 

 stomach after only having been subjected to a preliminary and partial 

 mastication in the mouth. It is then macerated by the fluids contained 

 in the stomach, and is again regurgitated to the mouth, to be subjected 

 to the final and complete process of mastication. . 



Rumination, or the returning of food from the stomach to the 

 mouth for a second mastication, is peculiar to polygastric herbivora. It 

 differs from vomiting in that the motion is perfectly voluntary, is a nor- 

 mal physiological process, and the matters regurgitated are again swal- 

 lowed without leaving the mouth. All true ruminants have a multiple 

 stomach, although all animals with multiple stomachs are not ruminants. 

 Thus, in the bird three stomachs may be described, and in certain ceta- 

 ceans, as well as in certain edents, as the sloth, the stomach may be 

 divided into a number of different compartments and yet rumination not 

 take place. 



The habits of ruminant animals necessitate some process by which 

 the food is hastily collected in a capacious paunch, to be again returned 

 to the mouth for mastication. Ruminant animals in a state of nature 

 instinctively rely on quickness of sight, acuteness of hearing, and agility 

 to enable them to elude their enemies. With a powerful prehensile 

 tongue, long and thick tufts of grass are rapidly carried into the mouth 

 and as rapidly swallowed. However tough the herbage may be, it is 

 slightly broken down by one or two strokes of the molar teeth ; it then 

 passes through the gullet into the capacious compartments which receive 

 the name of stomachs, but which are in reality pouches of the oesopha- 

 gus, and are situated between the latter tube and the true stomach. By 

 this arrangement herbivorous ruminants are therefore enabled to rapidly 

 stow away in these reservoirs a supply of food, where, on the approach 

 of danger, it maybe retained until an opportunity offers for its return 

 to the mouth, when it may be masticated at leisure. The stomach of 



