2i 4 E VOL UTION AND DISEASE. 



Bacteria using this term in a general sense require 

 high powers of the microscope and suitable methods of 

 preparation for their satisfactory detection and identifica- 

 tion : they appear as minute rods, or small rounded 

 bodies ; the latter are usually termed micrococci. In 

 order to prove that any given bacterium is the cause of 

 a particular disease, it is necessary to ascertain its 

 constant presence in the blood or tissues of animals 

 suffering from the disease, and then to cultivate it in 

 media apart from the living body through several 

 generations ; on introducing the product of such cul- 

 tivations into an animal, the disease should make its 

 appearance and the micro-organisms occur in the 

 lesions. 



Pathogenic bacteria, when introduced into an organism 

 either accidentally or designedly, give rise to trouble 

 which may be either local or general. The local signs 

 are peculiar, for the disease may in some cases be 

 restricted to the part at which the morbid agents were 

 introduced, or the tissues at the seat of inoculation may 

 serve as a focus in which the bacteria germinate and are 

 subsequently disseminated through the system generally, 

 producing profound disturbances and not infrequently 

 death. 



Before studying in detail the effects of the introduction 

 of bacteria into an organism, it will be necessary to 

 review the leading facts connected with the evolution of 

 the inflammatory process as manifested by a complex 

 organism. 



The simplest animal known the amoeba is a 

 microscopic mass of nucleated protoplasm capable of 



