34 6 DIGESTION 



usually found between ferments of the same kind derived from 

 different sources may be due to the presence of other substances, 

 and do not necessarily indicate that the ferments are distinct. For 

 the present it may be assumed that the amylase of saliva is the 

 same ferment encountered in the pancreatic juice, and in many, 

 or all, of the tissues. An oxydase or oxidizing ferment is also 

 present in saliva. The salts are calcium carbonate and phosphate 

 (often deposited as ' tartar ' around the teeth, occasionally as 

 salivary calculi in the glands and ducts), sodium bicarbonate, 

 sodium and potassium chloride, and almost always a trace of sul- 

 phocyanide of potassium, detected by the red colour which it strikes 

 with ferric chloride.* The total solids amount only to five or six 

 parts in the thousand. A great deal of carbon dioxide can be 

 pumped out from saliva, as much as 60 to 70 c.c. from 100 c.c. 

 of the secretion i.e., more than can be obtained from venous blood. 

 Only a small proportion of this is in solution, the rest existing as 

 carbonates. Oxygen is also present even in saliva which has not 

 come into contact with the air, and, indeed, in somewhat greater 

 quantity than in serum (about 0*6 volume per cent, in dog's saliva). 

 Under the microscope epithelial scales, dead and swollen leucocytes 

 (the so-called salivary corpuscles), bacteria, and portions of food, 

 may be found. All these things are as accidental as the last 

 they are mere flotsam and jetsam, washed by the saliva from the 

 inside of the mouth. But greater significance attaches to certain 

 peculiar bodies, either spherical or of irregular shape, that are seen 

 in the viscid submaxillary saliva of the dog or cat. They appear 

 to be masses of secreted material. The quantity of saliva secreted 

 in the twenty-four hours varies a good deal. On an average it is 

 from i to 2 litres (Practical Exercises, p. 454). 



Besides its functions of dissolving sapid substances, and so allow- 

 ing them to excite sensations of taste, of moistening the food for 

 deglutition and the mouth for speech, and of cleansing the teeth 

 after a meal, saliva, in virtue of its ferment, amylase, has the power 

 of digesting starch and converting it into the disaccharide maltose, 

 a reducing sugar (Ci^w^u)- ^ n man the secretion of any of the 

 three great salivary glands has this power, although that of the 

 parotid is most active. In the dog, on the other hand, parotid saliva 

 has little action on starch, and submaxillary none at all; while in 

 animals like the rat and the rabbit the parotid secretion is highly 

 active. In the horse, sheep, and ox, the saliva secreted by all the 

 glands seems equally inert. 



When starch is boiled, the granules are ruptured, and the starch 



* In 100 students the saliva only once failed to give the reaction, and in 

 this individual a trace of sulphocyanide was present 3 days later. It is absent 

 from the saliva of many animals. In 25 dogs submaxillary saliva obtained 

 by stimulation of the chorda tympanj only once gave the ferric chloride 

 reaction, and then faintly. 



