120 TEXT-BOOK OF BACTERIOLOGY. 



aside their noxious qualities and pass over into the ranks of the 

 innoxious bacteria. 



This apparently very striking- fact will become somewhat more 

 comprehensible if the causes of the pa.thogenic action of any given 

 micro-organisms are investigated. 



Here several possibilities must be taken into account. 



Examine with the microscope a stained section from the kidnej^ 

 of a Guinea-pig 1 which has died of anthrax. Look all through the 

 section, and everywhere innumerable rods will be seen. The capil- 

 lary vessels, and even the somewhat larger vessels, are filled with 

 bacteria which seem to have choked up the tissues. It will then 

 be understood why it is considered possible for the mere presence 

 of such masses to cause seriously deleterious results by their me- 

 chanical effect alone. 



In fact, the presence of so many foreign organisms can hardly 

 fail to injure the functions of the invaded organ, and when that 

 organ is so important as the liver, for instance, or the kidney, the 

 whole body is placed in the greatest danger. 



Yet this explanation is only possible for a small number of 

 cases. Frequently the mass of the bacteria is so insignificant that 

 such effects are quite out of the question. Almost always, too, we 

 cannot adduce clear proofs of the mechanical nature of such condi- 

 tions within the tissues. We may now and then find a ruptured 

 glomerulus which was unable to withstand the pressure of the 

 micro-organisms and was torn asunder by them. But all the 

 other effects which we might expect as the result of such an ex- 

 tensive stoppage of numerous vascular regions are wanting. There 

 is generally no appearance of hemorrhagic infarction or necrosis 

 of tissue such as we usually see after the formation of thrombi 

 and after embolic processes. 



We must, therefore, seek other causes for the peculiar action of 

 the pathogenic bacteria. 



The micro-organisms are living beings which require a definite 

 quantity of nutriment for their support. If they are parasitic they 

 take this nutriment from the organism which harbors them, and 

 which may be severely injured thereby. If the tribute exacted by 

 the parasite exceeds the amount which the victim can pay, if he 

 loses more in this way than he can make up in other ways, he 

 must, if no help comes, perish sooner or later. 



This tribute may be of different kinds. The chief kind, however, 

 consists of the albuminous substances, the material of which cells 

 are built, and which, as we already know, are a favorite food of the 

 bacteria. With these must be mentioned oxygen, which the 



