THE BACTERIA OF THE NORMAL HUMAN BODY. 153 



bacteria acting on particles of food about the teeth produce 

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

 According to Miller, bacteria play an important part in the 

 production 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 decalci- 

 fied matrix is then accomplished by other and liquefying 

 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. 



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 con- 

 tain 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 man- 

 ner as the gonococcus (pseudo-gonococci). 



There has been much dispute as to whether or not the 

 pyogenic bacteria occur in the vagina normally. It is prob- 

 able that the healthy vagina is in most cases free from the 

 pyogenic bacteria ; although bacteria of some sort are always 

 present, and the pyogenic bacteria may exceptionally be 

 found there in health. The normal secretion of the vagina 

 has a bactericidal influence which may be attributed in part 

 to its acidity. The upper part of the normal cervix uteri is 

 sterile, while bacteria are present in the lower part. 



According to Doderlein the properties of the vaginal secretion are 

 due to bacilli which very commonly occur in it. The secretion is most 

 abundant and important during pregnancy. 1 



T J. W. Williams, "Obstetrics, A Text-Book, etc.," 1903, pp. 34, 773- 

 7/5. Wadsworth, American Journal of Obstetrics, Vol. XLIIL, 1901. 



