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 



