SALIVA 245 



Mett employs the following method of determining the strength of a pro- 

 teolytic enzyme in a digestive fluid. Fresh white of egg is sucked into a narrow 

 glass tube, the tube is dipped into water at 95 and is then allowed to cool 

 slowly. The tube is now broken into small pieces and one of them is placed 

 in the fluid to be tested. The number of millimeters of the coagulated albumin 

 dissolved in a unit of time affords a measure of the enzymotic action. Amyloly- 

 tic action can be determined in a similar way by means of tubes containing 

 colored starch paste, and lipolytic action by finding the amount of fatty acids 

 set free in a given time from a known quantity of neutral fat. 



2. SALIVA 



Saliva is secreted by the three pairs of large salivary glands located in 

 the neighborhood of the buccal cavity and opening into it by their several 

 ducts, and also by small glands embedded in the mucous membrane of the 

 mouth. 



The product has a varying constitution according to the gland by which it 

 is formed,, and on the basis of the characteristic properties of their secretions 

 the salivary glands may be divided into two chief groups. One group, called 

 albuminous glands, produce a thin, watery secretion, which contains only pro- 

 teids, salts, and in certain cases a diastatic enzyme. Here belong the parotid 

 gland of all mammals, the submaxillary of the rabbit, some of the glands in 

 the nose and tongue, and the lachrymal glands. The other group the mucous 

 glands secrete a more or less viscid fluid, which contains mucin as its char- 

 acteristic ingredient, besides salts and small quantities of proteid. This group 

 includes the submaxillary glands (with few exceptions), the sublingual, part 

 of the buccal glands, those in the mucous membrane of the pharynx, the 

 larynx, trachea and oesophagus. There are also mixed glands e. g., the sub- 

 maxillary of man in which a part of the gland conforms to one of these types, 

 and a part to the other. 



The mixed saliva of man is a colorless or light-bluish, turbid, odorless, 

 slippery and viscid fluid, which upon standing for a time separates into an 

 upper, transparent and a lower, turbid layer, the latter consisting of mucous 

 flakes, salivary corpuscles, epithelial scales from the mouth, etc. The reaction 

 as a usual thing is weakly alkaline although it may be neutral, or even weakly 

 acid. It is asserted that the reaction early in the morning is weakly acid, 

 neutral or amphoteric, that after every meal it becomes alkaline and then 

 gradually returns to the neutral or weakly acid reaction. The specific gravity 

 is 1.002-1.009. 



The chief constituents of mixed saliva are: proteid, mucin, a diastatic 

 enzyme (ptyalin), and potassium sulphocyanide (KCNS). 1 Besides, we find 

 inorganic salts, gases and traces of ammonia, nitrous acid, urea, etc. Certain 

 drugs also are removed from the blood in the salivary secretion. 



According to recent analyses, the human saliva contains 98.8-99.5 per cent 

 water, and 0.5-0.2 per cent solids of which 0.1-0.4 per cent is organic; the 



1 We can only say with regard to this substance that its N and S probably come from 

 proteid. It has been assumed to confer an antiseptic action on the saliva, but this is not 

 confirmed. 



