258 The Physiological Role of Saliva 



which has always attracted great attention was at an early stage 

 supposed to have an antibacterial function ; the evidence in favour 

 of this view does not seem convincing. The bacterial flora of the 

 saliva in the mouth has been assumed to exert an antagonistic 

 action against pathogens. According to Bjornesjo (1950) this is 

 connected with a competition between the salivary bacteria and 

 pathogens for essential growth factors in the saliva. Other investi- 

 gators have assumed the oral flora to produce agents which inhibit 

 some other bacteria. Such an agent which has been discussed is 

 hydrogen of peroxide (Hegemann, 1950; Bethge, Soehring and 

 Tschesche, 1947). Bacteria producing peroxide have been found 

 to be present in samples of saliva (Hegemann, 1950; Kraus, 

 Nickerson, Perry and Walker, 1957). Since, however, saliva con- 

 tains peroxidase and catalase (Nickerson, Kraus and Perry, 1957; 

 Wolfe and Turner, 1957) the role of peroxide as an inhibitory agent 

 has been questioned (Bonicke, Reif and Arndt, 1953). Products 

 from the leucytes of saliva have also been supposed to contribute 

 to the antibacterial action of saliva (Willstatter, Bamann and 

 Rohdewald, 1929; Knorr, 1941 ; Dold, 1942). In 1922 Fleming 

 discovered an agent in tissues and secretions capable of dissolving 

 certain bacteria. It behaved like an enzyme and was called lysozyme. 

 The salivary lysozyme is not produced by bacteria but is an original 

 component of saliva (Chauncey and Lisanti, 1953). Its concentra- 

 tion is higher in combined submaxillary and sublingual than in 

 parotid saliva of humans (Hoerman, Englander and Shklair, 1956). 

 Saliva of most animals investigated contains lysozyme (Goldsworthy 

 and Florey, 1930). 



One complicating factor is that salivary mucin seems to diminish 

 the activity of lysozyme (Simmons, 1952). The virulence enhan- 

 cing effect of mucins has long been recognized and made use of in 

 experimental bacteriology. Smith (1951) demonstrated that mucin 

 preparations from human saliva increased the virulence of Bad. 

 typhosum in mice, probably by acting on the defence mechanisms 

 of the host. Bacteria and mucin were given intraperitoneally and 

 the experiments were not taken as evidence to show that mucin 

 actually aids pathogens in their attack on mucosal surfaces. 



Since saliva has been found to act against some pathogens which 

 are not affected by lysozyme, for instance diphtheria bacilli, many 

 investigators have concluded that other antibacterial agents than 

 lysozyme are present and probably produced by the salivary glands 



