548 THE BOOK OF THE DOG. 



become roughened and inflamed. The membrane itself is a closed bag, suited exactly to the 

 size of the surfaces it is meant to intervene. The inside of this bag, which is of a fibrous nature, 

 is very thin, and exceedingly smooth, and secretes a sort of lubricating mucus which makes it still 

 more smooth. 



Now, this serous bag, with its smooth well-lubricated inside, being firmly attached by its 

 outsides, it is not the actual surface of the bones that move against each other, but the smooth 

 inner sides of the serous sac. The intestines are guarded by a protecting bag of this sort, called 

 the peritoneum, a portion of which envelops every organ beneath the diaphragm or midrif, as the 

 liver, spleen, pancreas, kidneys, &c. The heart has a serous sac to itself, so have the lungs 

 (two, in fact) ; wherever, in a word, there are two opposing surfaces and motion, a serous 

 membrane intervenes to do away with the danger from friction. 



Now, in the joints these membranes are termed synovial membranes, that around the 

 heart the pericardium, and those around the lungs the pleurae. They are subject to inflam- 

 mation, these membranes, and when so inflamed they pour out a large quantity of serous 

 fluid, which fills and swells out the sac, and constitutes a dropsy. 



The internal surface of the small intestine is distinguished first by a number of longi- 

 tudinal folds, which are unfolded when the gut is distended, and it is covered throughout its 

 whole length with villi and follicles. 



The villi are so numerous on some portions of the internal surface of the small intestine, 

 that it presents the appearance of the pile on velvet. 



Each villus, as in the stomach, is surrounded by a net-work of blood-vessels, and each 

 villus has its own absorbent -vessel. 



The follicles are little sacs opening on the internal surface of the intestine, their use 

 being to secrete. 



Beneath the mucuous membrane of the duodenum, and opening on to its surface, are 

 some small globular bodies (Brummer's Glands) ; also Lieberkiihn's Glands, or simple follicles 

 in the mucuous membrane, and which open on the free surface of the intestine. They are 

 tube-like in shape, but microscopic in size. 



The solitary glands, found chiefly in the large intestine, are bigger, and easily seen. 

 They are round bodies, and around each is a circle of villi. Then we have what are called 

 " Peyer's Patches," or " Peyer's Glands," which are simply a collection of the solitary glands. 

 These patches of glands vary in number in the dog about from fifteen to twenty-five, and 

 some are half an inch or more in diameter. 



The large intestine is composed of the caecum, a blind sac, opening into the intestine 

 (said in ruminants to act as a reservoir for water). It is small in the dog, and somewhat 

 twisted, yet it is sometimes the seat of inflammation. Next comes the colon ; and, finally, 

 the rectum, which ends with the anus or outer opening, surrounded by a circular muscle, the 

 sphincter ani, which naturally is in a state of contraction. 



The intestines of the dog are comparatively short, and the colon, indeed, is little more 

 than a continuation of the small intestine. 



And now, just a few words on digestion itself. When a dog is hungry, and sees his 

 food, " his mouth waters." This is a common saying, and a true one ; and the explanation is 

 this : The glands which secrete the saliva are large in the dog the submaxillary is larger 

 even than the parotid they are, moreover, easily excited by the imagination to secrete, and 

 secrete largely too. When eating, this saliva speedily mixes with the food in the mouth, 

 rendering the necessity for slow mastication null. 



