RELATION OF BACTERIA TO DISEASE. 93 



in such enormous numbers as to interfere mechanically 

 with the circulation or cause minute thrombi, and later 

 emboli, which finally produce infarction and abscesses 

 in different parts of the body. These dangerous effects 

 are chiefly due, first, to their alteration of the nutritive 

 substances in the body into others which are valueless, 

 and, second, to their production of substances which 

 are more or less directly poisonous. 



A moment's consideration of the different changes 

 which take place in the tissues after the injection of 

 fine sterile sand and of an equal quantity of a dead 

 culture of the tubercle or typhoid bacillus would suf- 

 fice to convince any one that it was the poison produced 

 by the bacillus, and not its mechanical interference, 

 which caused disease. These poisonous products, as 

 already described in the previous chapter, can be 

 separated from the culture fluid in which the bac- 

 teria have grown or they can be extracted from their 

 bodies. These products without the bacteria them- 

 selves injected into animals cause essentially the same 

 lesions as are produced by the bacteria when they de- 

 velop in the animal body. When the body, as a whole, 

 is invaded by bacteria the abstraction from the body 

 of such substances as they consume exerts probably a 

 considerable influence; but even here it is the poisons 

 elaborated by bacteria from the body substances and 

 given up to the blood and tissue cells which are of most 

 importance. The substances contained in or produced 

 by the bacteria, with few exceptions, attract the leuco- 

 cytes, and when great masses of bacteria die suppura- 

 tion usually follows. 



The General Symptoms Caused by Bacterial Poisons 

 Absorbed into the Circulation. Fever is produced under 



