ORGANS OF DIGESTION. 325 



surface, and thus to prepare it for the action of the gastric 

 juice in the fourth stomach, to which organ we now trace it. 



In the young animal living entirely on its mother's milk, 

 the fourth is the only stomach employed ; it is, therefore, 

 then fully developed, whilst the others are small and imper- 

 fectly formed. The milk contains the elements of nutri- 

 tion in a much more perfect state than it exists in vegeta- 

 ble food. It requires but a little separation in order to fit it 

 for nutrition. As the young animal gradually becomes in- 

 ured to other food, the other stomachs become more devel- 

 oped. By the time the food reaches the abomasum it is in a 

 macerated pulpy state, and fit to be exposed to the powerful 

 solvent action of the gastric juice. This fluid is secreted in 

 abundance by the mucous coat of the fourth stomach. It is 

 a peculiar fluid, acid in its nature, and so powerful a solvent 

 that it has been known after death to dissolve a portion of 

 the coats of the stomach itself. It has in its composition 

 hydrochloric acid, and its action on the food is of a chemical 

 nature, converting it into chyme and rendering it into a fit 

 state for the other digestive processes. The food being thus 

 dissolved passes through the pyloric opening into the small 

 intestines ; this orifice has a valve-like construction (see p. 

 320), admitting the food to pass in one direction only, and 

 then not until it has been sufficiently acted on by the gastric 

 juice. 



The small intestines are of considerable length in the 

 sheep, being upwards of sixty feet. In the human subject 

 it is customary to divide them into three portions, and they 

 are called the duodenum, the jejunum, and the ileum. These 

 distinctions are arbitrary even in man, but still more so in 

 the sheep, and, in fact, cannot be properly applied. The 

 first portion of these intestines (the duodenum in man) dif- 

 fers much from the rest. It lies comparatively loose, and 

 on opening it we observe a yellow substance, which is, in 

 fact, the bile, which enters by a duct or very small tube 

 some eighteen inches from the stomach, and at nearly the 

 same place another fluid flows in from the pancreas or 

 sweetbread. These fluids, it may be supposed, exercise an 

 important office in the process of digestion, and the early 

 portion of the small guts is the situation where the admix- 

 ture takes place. 



The liver is a bulky organ whose size, general appear- 

 ance, and shape must be familiar to most people. Its weight 



28 



