26 THE NATURE OF INFECTION 



quently cited as an example of the possibility of infection through 

 intact epithelium. But we know that filtrates of gonococcus cultures 

 are in themselves capable of producing a mucopurulent inflammation 

 of the human urethral mucous membrane, so that here again no 

 proof has been afforded that the organism can infect through intact 

 epithelium. It is true that the bacterium itself seems to be capable 

 of causing the break in the integrity of the epithelium through its 

 own products, but there is also ground for the belief that this break 

 must first occur before actual infection can take place. With such 

 an organism as the gonococcus the question may of course be right- 

 fully asked whether it can ever occur on the mucosa of the urethra 

 without causing infection ; in other words, whether primary invasion 

 may ever occur without being followed by infection. The possi- 

 bility unquestionably exists, for we may conceive that the organism 

 in order to multiply sufficiently to cause damage by its own products, 

 must first find a suitable soil for its growth, and that this soil may 

 after all be furnished at some break in the continuity of the epithelial 

 covering. 



In the case of the diphtheria bacillus this is very likely, for we know 

 that the toxin production of this organism is fairly constant and that 

 there is no ground for believing that toxin is not formed by those 

 bacilli which may at times be found in the throats of perfectly 

 healthy individuals. As the amount of toxin is, however, evidently 

 not sufficient to cause local necrosis, we must assume that conditions 

 for active multiplication of the organism are not favorable, and we 

 can readily believe that a break in the continuity of the epithelium 

 at some point might be the essential factor which would lead to an 

 actual infection. This break may occur through mechanical means, 

 but it may also occur through the intervention of associated patho- 

 genic agents, and I would emphasize particularly the importance of 

 underlying pyogenic infections, for the occurrence of which the ground 

 is especially favorable in the lymphadenoid structures of the fauces 

 and the nasopharynx. 



The importance of such associated infections cannot be overesti- 

 mated. We have good evidence to show that in their absence, infec- 

 tion with certain bacteria cannot occur at all. It is thus well known 

 that the tetanus bacillus cannot maintain itself, when inoculated by 

 itself into perfectly normal tissues, while the simultaneous intro- 

 duction of pyogenic organisms renders its growth and multiplication 



