184 
ACT OF RUMINATION. 
here that we find the curious arrangement of water-cells in the 
stomach of the Camel, by which that animal is enabled to 
retain a supply of water for several days. These cells corre¬ 
spond with the little pits which are seen in the honey-comb 
stomach of the Sheep, but are much deeper, and their orifices 
may be closed by the action of a set of muscular fibres which 
pass in every direction round each, so as to form a net-work 
including these orifices in its meshes. 
199. After the food has been macerated in the fluids of the 
first and second stomachs, it is returned to the mouth by 
a reversed peristaltic action of the oesophagus, which brings 
it up as a succession of globular pellets, that are formed by 
compression in a sort of mould at the lower end of the oeso¬ 
phagus. These pellets are subjected within the mouth to 
mastication and insalivation; and the food is then ready for 
the real process of digestion. It is this mastication which is 
commonly known as the “ chewing of the cud; ” and the 
animal, whilst performing it, seems the very picture of placid 
enjoyment. When again swallowed, the food is directed, by 
a peculiar valvular groove at the bottom of the oesophagus, 
into the third stomach, commonly termed the many plies, 
from the peculiar manner in which its lining membrane is 
arranged. This presents a number of folds, lying nearly close 
to one another, like the leaves of a book, but all directed, by 
their free edges, towards the centre of the tube,—a narrow 
fold intervening between each pair of broad ones. The food 
has, therefore, to pass over a large surface, before it can reach 
the outlet of the cavity; and this leads to the fourth stomach, 
commonly termed the reed. This is the seat of the true digestive 
process, the gastric juice (§ 204) being formed here only ; 
and it is from this that the rennet is taken, which is used 
in making cheese to cause the milk to coagulate or curdle. 
In the sucking animal, the milk passes directly into this 
fourth stomach, without entering either the first or second 
stomachs, and without being delayed in the third, the folds 
of which adhere together so as to form a narrow undivided 
tube. The paunch is at that time comparatively small, being 
of less size than the reed; and its dimensions increase, as 
soon as the young animal begins to distend it by swallowing 
solid vegetable matter. 
200. In the digestive apparatus of .Birds, we find a con- 
