Protective Functions 257 



by 85 per cent by this procedure; the remaining activity was 

 assumed to be due to enzyme from already disintegrated cells. 



The role played by some other enzymes found in saliva, such as 

 lysozyme and kallikrein, will be discussed later in this chapter. 



PROTECTIVE FUNCTIONS 



The importance of protective functions of saliva for the health 

 of the teeth has already been mentioned. The oral mucosa is like- 

 wise dependent on an adequate flow of saliva. The stomatitis which 

 may appear during fevers is generally assumed to be related to a 

 reduced salivary secretion. There is some experimental evidence 

 to show that salivation may be diminished in fevers. Barbour and 

 Freedman (1921) found that fever, brought about by injection of 

 coli vaccine in dogs, reduced the salivary response to pilocarpine. 

 Koropow (1934) produced fever in dogs by injecting turpentine 

 and found the conditioned salivary reflex to diminish markedly; 

 the unconditioned reflex and the response to pilocarpine were not 

 affected. To a great extent the protective action of saliva is no 

 doubt simply due to the fact that the mucosa is kept moist and 

 lubricated and the mouth continuously rinsed by a permanent 

 stream of saliva, for even between the meals saliva is flowing 

 slowly. During sleep the secretion may be very small and possibly 

 confined to a spontaneous activity in some glands. When food is 

 eaten the rate of flow increases enormously. This is, of course, 

 connected with the digestive functions of saliva ; but an increased 

 protective action must also be required during a meal. Excessively 

 hot food is diluted and cooled by saliva, irritating or injurious 

 agents diluted, acids or alkali dealt with by the buffers of saliva 

 (see Sellman, 1949). 



The protective actions of saliva are also apparent during vomit- 

 ing. In the stage of nausea, which usually precedes the emptying 

 of the stomach, salivary secretion is very pronounced, as can be 

 concluded from the frequent swallowing. When the gastric con- 

 tents are expelled, saliva protects the mucous membranes. 



Much attention has been paid to the antibacterial action of saliva. 

 Many investigators have assumed that saliva acts not only by wash- 

 ing away bacteria, and food particles and desquamated cells which 

 could serve as substrates, but that saliva in addition possesses 

 specific bacteriostatic or bactericid properties. A great variety of 

 possible mechanisms has been proposed. The thiocyanate of saliva 

 p.s.g. — s 



