EXPERIMENTS ON DIGESTION. 363 
is formed into masses of a certain volume, the masticatory organs 
dividing it into particles more or less minute. 
Comparative anatomy teaches us, that the conformation and the 
disposition of the masticatory organs present, in the various orders, 
families, and species of the mammalia, differences which have evi- 
dent relation to the nature of the food, and the habits of each. 
Into the consideration of this, however, we shall not at present 
enter, but shall only observe, that in the dog and the cat the teeth 
are crowned with points more or less acute, or are decidedly 
trenchant, and that the temporo-maxillary articulation is so con- 
structed that the movement of the lower jaw is confined to a sim- 
ple up-and-down vertical action. Thus the aliment is divided, or, 
as it were, cut by the two branches of a pair of scissors, rather 
than crushed. In the horse and the ruminant, on the contrary, 
none of the molar teeth have a trenchant or pointed crown, but, 
are flattened and furrowed, and the disposition of the temporo- 
maxillary articulation permits to the lower jaw not only a verti- 
cal, but an horizontal action. Therefore these animals bruise and 
crush and grind their food while they are masticating it. 
Whatever may be the structure and the disposition of the mas- 
ticatory apparatus, the comminution of the food is always of the 
greatest importance, as connected with digestion. 
1. It destroys, to a certain degree, the cohesion of the food, and its 
organic reticular organization, and reduces it to smaller masses, 
more proper and easy to be swallowed. 
2. It renders them more penetrable by the saliva, which moist- 
ens and softens, and even dissolves some of their principal con- 
stituents. 
3. It favours their dissolution by means of the gastric juice. The 
more they are attenuated by it, and converted into a pultaceous 
mass, the more readily are they penetrated by the gastric juice, 
and the more perfectly it exercises its solvent power upon them. 
Action of the Saliva. 
During the act of mastication, the saliva mingles with the food. 
The secretion of this fluid is increased partly by the influence 
which the food exerts on the salivary glands, and partly by the 
motion of the masticatory organs. 
1. The saliva acts mechanically on the food. It moistens it, 
and forms it into a viscid mass easily swallowed. 
2. With the aid of the warmth of the mouth, it contributes to 
the dissolution of the food, as much by the great quantity of water 
which it contains, as by other solvent principles. Many simple 
aliments, as sugar, animal gelatine, and vegetable mucus, are 
