60 DIGESTION IN EUMINANTS. 



vies or paunch; c, the reticulum or honey-comb stomach; d, the omasum, 

 Di estive com- man 7pli es or third stomach ; e, abomasum, reed, or fourth 



partments of stomach ; and y, the pylorus. The food, roughly triturated 

 in the mouth, enters the ingluvies, in which it is moistened; 

 it then passes into the honey-comb or second stomach, which likewise 

 receives directly the water that has been taken, and, after it has been 

 thoroughly moistened therewith, it is returned to the mouth in small 

 portions, to undergo a more complete mastication and insalivation. Be- 

 ing swallowed again, it is now directed into the third stomach, from 

 which it passes into the fourth. In this it is submitted to a true acid 

 digestion, a gastric juice being secreted from the walls of this cavity. It 

 is the mucous lining of this cavity which yields rennet. That these com- 

 plicated motions and these successive actions of the different cavities are 

 for the purpose of preparation for the true digestion of the fourth stom- 

 ach, is clearly proved by the fact that in the calf the milk passes directly 

 into the abomasum. 



Since fishes and water animals generally have no salivary glands, or 

 Digestion on ty rudimentary ones, some physiologists have inferred that the 

 in fishes. use o f the saliva is for the commingling of the food with a due 

 portion of water. This would reduce the importance of insalivation very 

 greatly, and, indeed, is scarcely consistent with the elaborate mechanism 

 which has been just described in the case of ruminant animals. It is 

 worthy of remark that, even among fishes, there are some which exhibit 

 a true rumination, as, for example, the carp. This is not alone for the 

 purpose of resubmitting the food to the abrading action of the pharyngeal 

 teeth, but likewise for commingling it with the secretion of the pharyn- 

 geal cavity. 



In view of the preceding facts, it may be concluded that, so far from 

 there being any thing in contradiction to the doctrine that different por- 

 tions of the digestive surface of the mucous membrane of the stomach are 

 devoted to different duties, there is strong evidence in support of its truth, 

 derived partly frpm the instances furnished by comparative anatomy, and 

 partly from the anatomical structure of the gastric mucous membrane. 

 The four separate digesting chambers of the ruminating herbivora are 

 merely an elaboration of the structure which is presented by an appar- 

 ently homogeneous mucous surface in man. But that this mucous sur- 

 face is in reality heterogeneous, and in different regions possesses differ- 

 ent powers, is shown by the fact that at one part it presents mucous fol- 

 Reo-ionai func- ^ c ^ es at another pepsin follicles, at another follicles for the 

 tions of human secretion of hydrochloric acid. As we approach toward the 

 pylorus, the existence of a new function is betrayed by the 

 appearance of a new mechanism the villi, which have been so well stud- 

 ied by Dr. Neill, and this is even indicated externally in the posterior 



