50 PHYSIOLOGICAL REMAKES. 



is impossible to do more than glance at their various offices and 

 structures; I shall, therefore, simply describe the alimentary 

 canal as divided into the gullet, the stomach, and the small and 

 the large intestines all being lined with mucous membrane, which 

 again is covered by muscular fibres for the purpose of propelling 

 the contents of the stomach and intestines, and in the greater part 

 of the course of the canal by a smooth serous membrane (the 

 peritoneum) to allow the different viscera to roll easily one upon 

 the other. Now it is highly important to remember these three 

 general coats (as they are called), because their diseases are 

 different, and require totally opposite treatment. 



The food, being seized by the jaws of the dog, is, if of great 

 bulk, rapidly torn into such pieces as can be swallowed, and, in 

 the natural condition of the animal, prior to his domestication, 

 such a process would exercise the jaws very considerably, so as to 

 call upon the salivary glands to pour out their secretion in great 

 quantities ; but when the food is offered to him in a divided state, 

 which prevents all necessity for using the jaws, some other means 

 for procuring this necessary fluid must be provided, and this can 

 only be done by the use of bones, for him to gnaw. The food, 

 when swallowed, passes down the gullet into the stomach, which, 

 in the dog, is of considerable size, and will in a large greyhound 

 hold four or five pounds of food tolerably well ; this organ, as is 

 well known to everybody, is the main agent in digestion. Now, 

 by digestion, we understand the reduction of food by the gastric 

 juice (which is secreted by the stomach), so as to render it fit to 

 be taken up by the absorbents and conveyed into the blood ; this 



