1 62 MANUAL OF BACTERIOLOGY. 



bacteria acting on particles of food about the teeth produce the 

 bad odor from the mouths of persons of careless habits. Ac- 

 cording to Miller, bacteria play an important part in the pro- 

 duction of dental caries. Certain of the bacteria of the mouth 

 produce fermentation in the vicinity of the teeth with the 

 formation of acids, which dissolve the calcium 'salts of the 

 teeth. The softening and destruction of the decalcified 

 matrix is then accomplished by other forms. 



The expired air coming from the mouth and nose, con- 

 trary to the popular notion, is free from bacteria, excepting 

 those which become forcibly detached, as by efforts. of sneezing 

 and coughing. 



McKee* found that in the great majority of normal con- 

 junctivas the ordinary pyogenic bacteria and the bacillus 

 xerosis are present. He quotes Eyref as saying that the con- 

 junctival sac frequently contains bacteria which may or may 

 not be pathogenic; but, on the other hand that it may be 

 sterile, due to the mechanical flushing of the mucous surface 

 by the lachrymal secretion, aided perhaps by the bactericidal 

 property of the latter. 



Among the other exposed mucous "surfaces, the urinary 

 meatus and the vagina may be included. The urinary meatus 

 and at least part of the urethra will be found to contain bacteria, 

 which, in health, should be non-pathogenic, although interest 

 attaches to the fact that diplococci have been described which 

 behaved with stains in the same manner as the gonococcus 

 (pseudogonococci) . 



There has been much dispute as to whether or not the 

 pyogenic bacteria occur in the vagina normally. But there 

 appears abundant evidence going to show that while the vagina 

 may be free from pathogenic bacteria it often if not usually 

 harbors pyogenic bacteria. While it is true that the normal 



*Reprint from Montreal Med. Journ. Jan., 1906. 



^Lancet. Dec. 21. 1895. Journ. Pathol. and Bacter. July, 1896. 



