RELATION OF BACTERIA TO DISEASE. 95 
Bacteria also produce secondary poisons, which stand 
a temperature of 100° to 120° C. 
The Influence of Quantity in Infection. With bacteria 
the number introduced has an immense influence upon 
the probability of infection taking place. 
If we introduce into a culture medium, which, like 
the body, is only fairly suitable for growth, a few 
bacteria, it is not improbable that they may all die; 
whereas if a greater number are introduced, while there 
will at first be a slight diminution of these, those that 
die seem to neutralize the substances which were dele- 
terious; then those bacteria which survive begin to in- 
crease, and soon they multiply enormously. The same 
is true for parasitic bacteria in the body. A few only 
gaining entrance, they may die; a larger number being 
introduced, some may or may not survive; but if 
a still greater quantity is injected it is almost certain 
that there will be some surviving members, which, after 
the destruction of antagonistic substances, and on be- 
coming accustomed to their environment, will begin to 
grow and produce disease. 
With those bacteria whose virulence is great—i. ¢., 
those which are capable of growing with great ease in 
the body fluids—a very few organisms will produce 
disease almost as quickly as a million, allowance only 
being made for the short time required for the few 
to become equal in number to the million. At the 
other extreme of virulence, however, many millions 
may have to be introduced to permit of the develop- 
ment of any of the organisms in the body. With these 
bacteria we are thus able to produce either no effect 
whatever, a local effect, or in some cases a general sep- 
ticemia, by regulating the amount of infection intro- 
