RESISTANCE OF ORGANISMS. 



115 



A eilcies ' 



amount to virtual thrombosis. Filariae, which are 

 multicellular organisms, cause grave conditions by 

 occlusion of the lymphatics. 



In discussing the second condition for the occur- 

 rence of infection, namely, the ability of the 

 micro-organism to remain alive and to proliferate 

 in the body of the host, this must be done with 

 regard to certain protective agencies which the host 

 possesses against invading micro-organisms. 



As will appear later in more detail, these agencies Anti- 

 may be directed either against the toxins of the 

 micro-organisms, or against the parasitic cells 

 themselves. The former rests in the antitoxins 

 which may be present in the plasma and lymph, 

 and the power of the tissues to bind and destroy 

 the toxins; the latter in the germicidal substances 

 of the body fluids (the so-called bacteriolysins), 

 and in the phagocytic and destructive action of 

 various cells of the body, particularly the leucocytes 

 and endothelial cells. Manifestly, in actual infec- 

 tion the micro-organisms are able to proliferate in 

 spite of the presence of these antagonistic agencies, 

 and the conditions which render this possible prob- 

 ably vary a great deal in different infections. 



Thus, in relation to tuberculosis, either the 



_ . .. . . -, i 



serum of man and animals possesses no germicidal 

 substances for this particular organism, or the lat- 

 ter is resistant to their action. Also, since the 

 bacilli are frequently found within phagocytic 

 cells in a good state of preservation, it would 

 seem that they have a certain degree of resistance 

 to intracellular digestion. Staphylococci, strepto- 

 cocci and certain other organisms resist destruction 

 by the serum, although they are readily taken up 

 and destroyed by phagocytes. 



Natural 



Resistance of 



organisms. 



