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 
