62 ESSENTIALS OF BACTERIOLOGY. 



subtilis or some other aerobic germ. The subtilis does not allow 

 the oxygen to pass by, appropriating it to itself. 



Buchner's Method. The test tube containing the culture 

 is placed within a larger tube, the lower part of which con- 

 tains an alkaline solution of pyrogallic acid or some other agent 

 which absorbs oxygen. The tube is then closed with a rubber 

 stopper. (Fig. 37.) 



CHAPTER XIII. 



THE WAY IN WHICH BACTERIA AFFECT THE ANIMAL ORGANISM. 



BACTERIA affect the animal organism by depriving the cells 

 of the body of oxygen and nitrogen which they appropriate to 

 themselves for their maintenance. 



They do more than this, however, for in their secretions and 

 excretions the main potency lies. 



Ptomaines, or Cadaveric alkaloids, was the name first applied 

 to those bodies formed during putrefaction, but now used for 

 all alkaloids or bodies of a basic nature formed by bacteria. 

 Many of these ptomaines when introduced into the body give 

 rise to the same set of symptoms as the bacteria themselves do, 

 so that we may say, bacteria affect the animal body chiefly through 

 certain toxic principles which they produce and which can be isolated. 



Toxines and Toxalbumens. Late researches claim two classes 

 of products for bacteria the one toxic and destroyed by heat ; 

 the other anti-toxic, having a direct action upon the tissue and 

 preventing further infection. Then proteids or toxalbumens, 

 products extracted from pure cultures, which, like ptomaines, 

 produce symptoms similar to those of the bacteria itself. They 

 are amorphous and have no basic action, giving, however, all 

 the reactions of a proteid or albumen. 



Filtration of Cultures. These products are isolated from the 

 culture after the bacteria themselves have been separated. 



A filter consisting of a cylinder of porcelain, asbestos or 

 kaolin, through which the culture fluid passes, the bacteria 

 remainin^ behind, is called the Pasteur-Chamberland filter. 



