26 THE NATURE OF INFECTION 



direct or indirect communication with the exterior. This has long 

 been recognized and is well established. Organisms like the staphy- 

 lococcus and the streptococcus can thus exist on the intact skin with- 

 out giving rise to any disturbance whatever; they are evidently 

 unable to penetrate to the deeper structures through their own 

 efforts. The same manifestly holds good for the epithelial struc- 

 tures of the body in general; staphylococci and streptococci exist in 

 the intestinal tract as on the surface of the body without causing 

 any damage. If, however, the epithelial covering at the point is 

 broken and invasion at the point of injury has preceded, or has 

 occurred at the same time, infection of greater or less extent will of 

 necessity follow. In many instances of infection with the organisms 

 in question the break in the continuity of the epithelial covering 

 may be ever so slight, but it is very doubtful whether infection with 

 these organisms ever occurs through an intact epithelial barrier. 



To furnish examples of infection through the injured epithelial 

 coverings seems almost banal; but I would briefly recite the increas- 

 ing amount of evidence that so many cases of arthritis, formerly 

 ascribed to physical influences, vague hereditary tendencies, etc., 

 are now known to be infectious in origin, the portal of entry 

 being frequently a relatively small focus of inflammation in con- 

 nection with a tooth, the tonsils, the various sinuses, etc. Due to 

 similar peripheral local causes also are unquestionably many cases 

 of endocarditis with their manifold complications, pleurisy, pneu- 

 monia, nephritis, etc. 



While no evidence has thus far been presented to suggest the possi- 

 bility that infection with these organisms can take place through the 

 intact skin, various attempts have been made to prove that this is 

 possible in the case of other types of organisms. But I must confess 

 that the experiments in this direction do not carry conviction. 

 It has thus been argued that the intact skin must be permeable to 

 an organism like the plague bacillus, because the disease invariably 

 develops in guinea-pigs in which the organism has been rubbed 

 into the shaved abdominal surface. Such experiments demonstrate, 

 of course, that infection with the organism in question may be 

 effected through the skin; but they do not prove by any means that 

 infection takes place through the intact skin. Through the mere 

 process of rubbing slight injuries are unquestionably produced, if not 

 directly, then at least indirectly, for we can readily see that the 



