RELATION OF BACTERIA TO DISEASE. 91 
organic material under very diverse conditions, others 
only under specially favorable conditions. In the body 
they also vary—some grow extensively in the blood, 
while others are limited to one or more tissues, some 
being widely disseminated throughout the body, while 
others are localized in or upon a certain portion of it. 
3. Strict parasites, or bacteria which, so far as we 
know, grow only in the living animal or vegetable 
organism. These again vary in the amount of poison 
which they produce and in the local or general infec- 
tion they give rise to. 
Adaptation of Bacteria to the Soil upon which They are 
Grown. Those bacteria which grow both in living and 
dead substances vary from time to time as to their 
readiness to develop in either the one or the other. 
As a general rule, bacteria grown in any one medium 
become more and more accustomed to that and other 
' media more or less analogous to it, while, on the other 
hand, they are less easily cultivated on media widely 
different from that in which they have developed. Thus 
we have a culture of tubercle bacilli, which, after having 
grown for three years in the bodies of guinea-pigs, will 
no longer develop on dead organic matter, while a 
bacillus which was obtained from the same stock, but 
grown on bouillon for three years, will no longer de- 
velop in the animal body. From the same stock, 
therefore, two varieties have developed, the one being 
now practically a saprophyte and the other a parasite. 
The Local Effects Produced by Bacteria and their Prod- 
ucts. Nearly all the forms of acute inflammation are 
seen to follow the development of bacteria. Thus in- 
flammation and serous exudation into the subcutaneous 
tissues follow injections of the pneumococcus or anthrax 
