42 CLINICAL BACTERIOLOGY. 



Finally, it is also possible, as Nencki has shown, that two 

 microbes may produce an entirely new substance through 

 their influence upon the culture -medium, and which neither 

 of the two bacteria was alone capable of producing. Also, 

 the observation of Nencki's, so characteristic for the signifi- 

 cance of mixed infection, is to be borne in mind, that " sterile 

 solutions of grape-sugar, simultaneously injected with two 

 given bacteria, are much more rapidly and more energetic- 

 ally decomposed than by either of the two germs alone." 



(c) The Portals of Infection. Natural portals of in- 

 fection are constituted by all those parts already named 

 that communicate with the external world (p. 36). The 

 most important infectious agents are taken up with the in- 

 spired air and with the nourishment or through the skin. 

 The uninjured skin forms an insuperable barrier that can 

 be overcome only by vigorous inunction of bacteria in an 

 ointment-basis. It is possible, in this way, to produce fur- 

 uncles by the rubbing in of staphylococci, and general infec- 

 tion by the rubbing in of anthrax-bacilli or of glanders- 

 bacilli. If, however, a breach in the continuity of the skin 

 takes place, then the chances for the invasion of bacteria are 

 rendered much more favorable. Superficial cutaneous fis- 

 sures suffice to permit the bacteria of anthrax and of septi- 

 cemia to gain entrance into the organism. Deeper subcuta- 

 neous wounds are more dangerous, because the lax tissues 

 permit absorption in much greater , degree. Contused and 

 lacerated wounds, to which access of the oxygen of the air 

 is not unobstructed, favor the development of anaerobic 

 bacteria, especially that of tetanus. The absence of oxygen 

 appears, further, to constitute a favoring influence for the 

 activity of the ordinary pyogenic cocci. Recent wounds take 

 up microorganisms with remarkable rapidity through the 

 opened blood-vessels. Within as short a time as thirty or 

 forty minutes, bacteria, even saprophytes, placed upon a 

 fresh wound may be found within the internal organs. In 

 the case of old suppurating wounds, on the other hand, 

 absorption of microorganisms takes place only in quite 

 limited degree. 



The mucous membranes also, in an uninjured state, prove 

 not especially susceptible to bacterial invasion. If, how- 

 ever, a breach in the continuity of the epithelial covering 

 takes place, then opportunity is afforded for the entrance 

 and the absorption of the germs present. Exceptions to 



