INFECTION. 43 



the rules just cited are furnished by a number of mucous 

 membranes in relation to certain microorganisms. The 

 normal conjunctiva is, for instance, susceptible to invasion by 

 the gonococcus and also by the bacillus of intestinal diph- 

 theria. Upon the mucous membrane of the urethra like- 

 wise, only the causative agent of gonorrhea thrives. In the 

 mouth, according to the investigations of Sanarelli, only 

 two microorganisms develop properly : the diplococcus of 

 pneumonia and the bacillus of diphtheria. The tonsils, 

 however, with their markedly irregular surface, and with 

 their richly developed lymphatic structure, do not share in 

 the protection of the remainder of the mucous membrane 

 of the mouth, but, on the contrary, constitute a frequent 

 portal of entry for numerous infections. 



The gastric juice, by reason of the hydrochloric acid it 

 contains, is disinfectant and bactericidal, but this gastric- 

 juice hydrochloric-acid barrier has for a long time been 

 greatly overestimated. The permanent forms the spores 

 are not at all affected by the gastric juice, and the resistant 

 tubercle-bacilli in no greater degree ; and even less resistant 

 germs pass the pylorus so rapidly, especially after the 

 ingestion of large amounts of fluid, that the gastric juice 

 is not afforded sufficient opportunity to cause the death 

 of the microorganisms. The mucous membrane of the 

 intestine is far more markedly predisposed to infection. 

 The cause for this difference, as in the case of the tonsils, 

 must be looked for in the abundance of glands, of lymphatic 

 elements, and of the absorptive apparatus generally. 



Bacteria are, under certain conditions, absorbed from the 

 mucous membrane of the air-passages, and are then in- 

 tercepted by the bronchial lymphatic glands. Only in this 

 way is to be explained the not uncommon discovery of the 

 presence of tuberculosis of these glands, with complete 

 immunity of the lungs. The uterine mucous membrane is, 

 as may be readily understood, a most suitable surface for 

 the absorption of infectious agents during parturition and 

 also during menstruation. 



In animal experimentation subcutaneous, intravenous, 

 and intraperitoneal injections are especially employed. 

 Other methods of inoculation, such as the cutaneous, the 

 intraocular, the intracranial (subdural), etc., are employed 

 less commonly, and only for special purposes. In animal 

 experimentation the same amount of a culture exerts differ- 



