Immunity of the skin and mucous membranes 415 



It is often asked, how under these conditions does the mouth 

 defend itself against the vast number of formidable micro-organisms. 

 When the theory of the bactericidal power of the body fluids was 

 dominant, and appeared to explain several important points in the 

 general problem of immunity, the saliva was studied from this 

 "bactericidal" point of view. Sanarelli 1 , as the outcome of patient 

 and laborious researches, came to the conclusion that the human 

 saliva acted as an antiseptic and destroyed a large number of micro- 

 organisms. It is true that he recognised its efficacy only when few 

 bacteria were subjected to its action ; but even when the saliva was 

 incapable of killing a large number of micro-organisms, it did not 

 allow them to develop it was a bad culture medium ; moreover, it 

 had the power of attenuating the virulence of certain pathogenic 

 bacteria, such as the pneumococcus, so frequently found in the 

 mouth. 



The conclusions of the Italian observer did not, however, meet 

 with general acceptance. Miller 2 did not believe that the saliva 

 exerted any bactericidal action, raising the objection that the absence 

 of nutritive value in the human saliva for bacteria is explained by 

 the fact that in his experiments Sanarelli employed filtered saliva, 

 which consequently had been deprived of much of its nutritive 

 substances, epithelial debris, mucus, etc. Hugenschmidt 3 , working 

 in my laboratory, carried out a special research on the influence of 

 the human saliva on micro-organisms, and arrived at conclusions 

 quite at variance with those reached by Sanarelli. In spite of the 

 variety of micro-organisms made use of, he could never satisfy himself 

 that the saliva had any bactericidal property. 



He sometimes saw, no doubt, a certain slowness of growth or [436] 

 even the destruction of certain of the micro-organisms sown at the 

 commencement of the experiment, but this was very slight and 

 rather exceptional. In most cases the micro-organisms, introduced 

 into the saliva, grew rapidly, so that their number, in a very short 

 time, became very considerable. Where the saliva brought about 

 any diminution in the number of micro-organisms, this semblance 

 of bactericidal action could be noted not only in the normal saliva, 

 but also, as in the lachrymal secretion above described, in saliva 



1 " La saliva umana," Siena, 1891, and Centralblf. Bakteriol. u. Parasitenk,, Jena, 

 1891, Bd. x, S. 817. 



2 op. cit. 



8 Ann. de Hnst. Pasteur, Paris, 1896, t. x, p. 545. 



