LOCAL CONDITIONS AND INFECTION 23 



is a good deal of evidence to show that local conditions are of the 

 greatest importance in determining the occurrence or non-occurence 

 of infection. It is thus well known that infection with the cholera 

 vibrio, the typhoid or the dysentery bacillus can only occur from the 

 digestive tract, while the gonococcus shows a marked predilection for 

 the genital tract and the conjunctiva, and the meningococcus for the 

 upper respiratory tract. The staphylococcus and streptococcus, on 

 the other hand, as well as the plague bacillus may infect from almost 

 any point, and the same probably is true of the pneumococcus, 

 although its special affinity is directed to the respiratory tract. It 

 might be argued, of course, that the organisms in question do not 

 meet with more favorable conditions for infection at the points 

 where this usually occurs than would be the case elsewhere, and that 

 they infect from these points largely because they are the only regions 

 which are usually open to invasion. There is no good evidence, how- 

 ever, to support such a claim, while a number of data go to show that 

 there are unquestionably definite districts which are more prone to 

 become points of infection with specific organisms than others, because 

 of purely local conditions. The gonococcus and diphtheria bacillus 

 are thus incapable of producing an infection through the skin, even 

 when this has been previously wounded at the point of contact with 

 the organisms in question. The cholera vibrio can infect only from 

 the intestinal mucosa, but not from the mouth, the esophagus, the 

 stomach, or the genital tract. In the stomach, indeed, an active 

 multiplication of the organism in question cannot occur, as the 

 cholera vibrio is rapidly destroyed by the hydrochloric acid of 

 the gastric juice. 



While local conditions are thus unquestionably of moment in 

 determining a liability to infection and primary invasion on the part 

 of an organism, we still have no explanation why pathogenic organ- 

 isms may exist at these points without consequent infection. The 

 demonstration of certain preferences of localization for the growth 

 of an organism is, however, in itself an important point to establish, 

 for unless local conditions were such that the invader could at least 

 maintain itself, subsequent infection would of course be rendered 

 difficult. 



Infection from the normal stomach where hydrochloric acid is 

 being produced during many hours of the day, would a priori 

 seem to be a difficult matter. In consequence of the active 



