270 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



It is evident from the varied Sources of the buccal fluid that the 

 saliva is by no means a homogeneous fluid. If collected from the 

 mouth by expectoration, or in the lower animals by holding the mouth 

 open and stimulating the surface of the tongue and the cheeks by any 

 sapid substance, as by the vapor of ether or acetic acid, or even me- 

 chanically, the fluid poured out will be found to be opalescent or more 

 or less turbulent: with a decided froth on its surface, from the air- 

 bubbles retained through its viscidity, and when allowed to stand in a 

 glass will deposit a sediment of epithelial cells and the so-called salivary 

 corpuscles. It will, therefore, form three different layers : the lower 

 one composed of this deposited sediment ; the middle, of a clear, though 

 opalescent, watery fluid ; while the uppermost layer will be more or less 

 frothy. Where a specimen of saliva remains standing for two or three 

 days exposed to the air the froth will disappear, and its place be taken 

 by a thin pellicle of carbonate of lime. When filtered, saliva forms a 

 watery fluid with alkaline reaction. Occasionally, where it appears to 

 have an acid reaction, the acidity is due to the fermentation of some 

 retained fragments of food in the mouth, as occurs after prolonged fast- 

 ing in diabetes and other pathological conditions; the secretion of the 

 salivary gland is invariably alkaline. Frerichs states that 0.15 gramme 

 sulphuric acid is necessary to neutralize the alkalinity of human saliva 

 collected during smoking. 



The specific gravity of mixed saliva varies somewhat in different 

 animals. It has been placed at 1004.5 in the horse; 1010.2 in the pig; 

 1010 in the cow; 1007.1 in - the dog; and from 1002 to 1006 in man. 

 Deprivation of water is said to cause the saliva to acquire a higher 

 specific gravity ; thus, in the horse the normal specific gravity of 1004.5 

 or 1005, may be raised to 1007.4 after the animals have been deprived 

 of water for twelve hours. 



The amount of saliva varies very largely according to a number of 

 different conditions. Colin places the average daily secretion of saliva 

 in the horse at eighty-four pounds, and in the ox at one hundred and two 

 pounds ; while in the dog Jacubowitsch obtained in a hour 49.19 grammes 

 of parotid saliva, 38.94 of submaxillary and 24.84 of sublingual saliva. 

 We will, however, again return to the volume of saliva and the different 

 conditions modifying the rapidity of secretion when we come to con- 

 sider the secretion of the separate glands. 



When examined under the microscope mixed saliva is found to con- 

 tain numerous epithelial cells from the cavity of the mouth, often debris 

 of food, inorganic particles of tartar from the teeth, various forms of 

 minute bacterial organisms, and the so-called salivary corpuscles. The 

 latter closely resemble white blood-cells in appearance, but are somewhat 

 larger, and are nucleated protoplasmic cells without a cell-membrane. 



