ELIMINATION OF PATHOGENIC MICROORGANISMS 243 



MECHANISM OF ENTRANCE OF ORGANISMS. 



In the preceding chapters statements have been made 

 that "bacteria enter" at various places or they "pass 

 through" different mucous membranes, skin, etc. Strictly 

 speaking such statements are incorrect— bacteria do not 

 "enter" or "pass through" of themselves. It is true that 

 some of the intestinal organisms are motile, but most of the 

 bacteria which are pathogenic are non-motile. Even the 

 motile ones cannot make their way against fluids secreted 

 or excreted on free surfaces. Bacteria cannot pass by 

 diffusion through membranes, since they are finite particles 

 and not in solution. 



In the case of penetrating wounds bacteria may be carried 

 mechanically into the tissues, but this is exceptional in most 

 infections. Also after gaining lodgement they may gradually 

 grow through by destroying tissue as they grow, but this is 

 a minor factor. Evidently, there must be some mechanism 

 by which they are carried through. The known mechan- 

 isms for this in the body are amoeboid cells, especially the 

 phagocytes. It is most probable that these are the chief 

 agents in getting bacteria into the tissues through various 

 free surfaces. The phagocytes engulf bacteria, carry them 

 into the tissues and either destroy them, are destroyed by 

 them or may disgorge or excrete them free in the tissues or in 

 the blood. 



DISSEMINATION OF ORGANISMS. 



Dissemination of organisms within the tissues occurs either 

 through the lymph channels or the bloodvessels, or both. 

 If through the lymph vessels only it is usually much more 

 restricted in extent, or much more slowly disseminated, 

 while blood dissemination is characterized by the number 

 of organs involved simultaneously. 



PATHS OF ELIMINATION OF PATHOGENIC MICRO- 

 ORGANISMS. 



I. Directly from the point of injury. This is true in 

 infected wounds open to the surface, skin glanders (farcy), 



