178 MANUAL OF BACTERIOLOGY. 



another part of the body, and to cause the disease in the new 

 situation in the individual's own body. This is called auto- 

 infection. It is also the case that certain bacteria remain 

 inert when present in certain parts of the body, but cause dis- 

 ease when transferred to other parts. The microbes of lobar 

 pneumonia, for instance, flourish in the mouths of a large 

 number of people and under favoring circumstances may 

 produce disease in the lungs or other parts, though it is not 

 known in this case whether the infecting organism comes from 

 the patient's own mouth or from the outside. The bacillus 

 coli communis, which constantly inhabits the intestines, may 

 invade other organs and exhibit pathogenic properties when 

 the way is opened up for it by other disease processes. Persons 

 suffering from gonorrhea frequently infect their eyes by trans- 

 fering the urethral secretion. 



Bodily Conditions that Predispose to Infection. The 

 development of an infectious disease may be favored by certain 

 bodily conditions spoken of as predisposing causes. These 

 may be general and operate in such a way as to low r er the 

 general tone of the body, as it is rather vaguely stated; or may, 

 in addition, predispose to certain definite infection. Thus 

 hunger, cold and exhaustion make the body more liable to the 

 inroads of pathogenic bacteria in general; so also do anemia 

 and chronic diseases. As an example of predisposition to 

 specific infection is the well-known fact that those suffering 

 from diabetes are espiecially liable to infection by the pus- 

 producing bacteria and the bacillus tuberculosis. Prolonged 

 anesthesia probably renders patients who have undergone 

 operations more liable to surgical infections and to absorption 

 of bacterial poisons. Predisposition to infection may also 

 arise in such cases from auto-intoxication with the products of 

 (disordered metabolism of the patient's own cells. Some of the 

 above-mentioned conditions can be imitated in laboratory ex- 

 periments. Hens in a normal condition are not susceptible to 



