266 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



A cutting motion is required, fulfilled bj' the incisor teeth, which are 

 consequently most highly developed in the rodents; and a grinding 

 motion, accomplished by the molars. As we have already found, the 

 lower jaw is capable not only of elevation and depression, but also of 

 advancement, retraction, and rotation, and all these motions are required 

 in the mastication of food by the herbivora. This motion is unilateral 

 and may occur continuously on one side for fifteen minutes, and then 

 alternate to the opposite molars, and we shall find that the secretion of 

 the parotid salivary gland coincides with the side on which mastication 

 is taking place. This peculiarity of secretion is seen in all ruminants 

 and most herbivora, and has been even claimed to take place in man. 



The duration of mastication depends upon the natural group to 

 which the animal belongs, on its age, and therefore the condition of its 

 teeth, and the character of its food. Carnivora require but slight mas- 

 tication of their food, and, in fact, mastication, as seen in the herbivora, 

 may in them be said to be entirely absent, the movements of mastication 

 in carnivora being simply confined to tearing the food into pieces small 

 enough to be swallowed. The herbivora, from the nature of their food, 

 need a longer time for reducing it to a condition of fine comminution, 

 and we find among the herbivora differences in the duration of mastica- 

 tion, according as the animals are ruminant or non-ruminant. The non- 

 ruminant animals, such as the horse, chew their food thoroughly and 

 once for all. It has been estimated by Colin that a horse will require one 

 and one-fourth hours for the mastication of four pounds of dry hay, and 

 of this amount will make sixty to sixty -five boluses, and, accordingly, 

 sixty to sixty -five motions of deglutition, while the rate of mastication 

 will be about seventy to eighty strokes of the teeth per minute. If anj'- 

 thing interferes with the secretion of saliva the duration of mastication 

 will be very much prolonged. One of the main objects of mastication 

 in the herbivora is to aid in the maceration of the food. Where, as in 

 the solipede, the food must be thoroughly macerated and comminuted 

 before reaching the stomach, the duration of mastication will naturally 

 be much longer than in the ruminant, where the food is simply subjected 

 to a few strokes of the teeth and then swallowed, to then undergo pro- 

 longed maceration in the rumen of these animals, and to be again 

 subjected to a second mastication in the mouth. In both animals, 

 although in a more marked degree in the horse, suppression or inter- 

 ference with the flow of saliva will prolong mastication; again, the drier 

 the food the greater will be the amount of mastication necessary before 

 the food can be comminuted and macerated sufficiently to be swallowed. 

 Therefore, grazing animals will require a less degree of mastication of 

 their food than those which are fed on grains or dry fodder. In the 

 ruminant the first mastication is three times as fast as the mastication 



