60 THE RELATION OF BACTERIA TO DISEASE 



excessive hunger and thirst, by exposure to cold and 

 wet, or by prolonged muscular or mental strains. 



Conditions resulting after the entrance of bacteria 

 into the body may be defined as follows: Infection is 

 best considered as the presence of disease-producing 

 germs and the evidence of their effects. Intoxication 

 is the condition due to the poisons elaborated by 

 bacteria. Septicemia or bacteriemia is the presence of 

 the bacteria and their products circulating in the blood, 

 with some involvement of all the organs in the body. 

 Pyemia is similar to the last but includes the pro- 

 duction of many abscesses throughout the body. 

 Fever may be described as a disturbance by bacterial 

 poisons of the mechanism in the brain which controls 

 the heat of the body. 



Some bacteria merely multiply in the body and 

 exert their effect simply by their mechanical presence 

 without any peculiar poison. Others have the power 

 of elaborating poisons that are specific or individual 

 whose effect is added to that of the bacterial bodies. 

 The latter form the larger percentage, and it is with 

 them we shall deal chiefly. The ability of bacteria to 

 cause disease is spoken of as their virulence. Each indi- 

 vidual kind of bacterium produces only one form of 

 disease and always that one form. In the early 

 history of pathological bacteriology Koch elaborated 

 certain rules or postulates by which the relation of 

 bacteria to disease is determined. They are essentially 

 that the same bacterium should always be found in 

 the same clinical disease, produce this disease when 

 injected into animals, be recovered again from the 

 animals and retain its biological characters. By this 



