PATHOGENIC BACTERIA 233 



teria produce disease conditions without entering the tissues 

 of the body. For example, Msp. comma produces poisonous 

 effects on the mucous membrane of the intestines without 

 entering the tissues. 



The mere entrance of the bacteria into the body or the tissues 

 of the animal or plant is only a part of the process of infection. 

 In addition there must be some injury to the body cells. As 

 has been mentioned above, the harmless saprophytic bacteria 

 may be present in the body of an animal and never produce 

 any morbid effects until, for some reason or other, the resist- 

 ance of some of the body cells is reduced. The term " in- 

 fested " has been applied to those conditions where so-called 

 harmless bacteria are present in the body normally. These 

 bacteria may enter the tissues of the body under certain con- 

 ditions and produce an infection. Adami calls this process 

 subinfection. 



It has been stated that all diseases due to bacteria are in- 

 fectious. A certain proportion of these infectious diseases are 

 also contagious; that is, they may be transmitted by direct con- 

 tact of the infected individual with healthy individuals, or by 

 indirect contact through the agency of fomites. Contagion 

 has to do with the manner of transmission of a disease, and 

 infection with the nature of the cause of the disease. For ex- 

 ample, smallpox and diphtheria are infectious, contagious dis- 

 eases, while tetanus and anthrax are purely infectious diseases. 



Infectious diseases may be arbitrarily divided into specific 

 and non-specific diseases. Specific infectious diseases are those 



