ABILITY OF BACTERIA TO PRODUCE DISEASE 95 



case if the invaders retain their pathogenic powers the person 

 thus harboring them and probably disseminating them is termed 

 a germ " carrier." Thus pneumococci and influenza bacilli 

 are present in the nose or throat of many individuals. Persons 

 who have recovered from an attack of diphtheria or who have been 

 in contact with those suffering from the disease frequently become 

 carriers. The typhoid bacillus may remain located in the gall 

 bladder and be discharged in the feces long after all symptoms of 

 the disease have disappeared. It has been estimated that after 

 convalescence from typhoid fever one to three per cent may remain 

 carriers for months or years. 



When the balance of such a relationship is disturbed by dimin- 

 ished resistance on the part of the body infection is likely to occur. 

 Such an infection is spoken of as autogenous. Appendicitis result- 

 ing from infection by the colon bacillus following congestion due 

 to fecal impaction may be taken as an example. Usually, however, 

 infections result from contact with contaminated material outside 

 of the body. Probably those conveyed by water or food are of the 

 most frequent occurrence ; for example, typhoid bacilli or cholera 

 spirilla by water, tubercle bacilli by milk. Or infection may result 

 from a scratch with a rusty nail on which are the spores of tetanus, 

 or hydrophobia from the bite of a rabid dog. 



Infections resulting from the introduction of bacteria from 

 sources apart from the individual infected are spoken of as ex- 

 ogenous. 



Contagious and Infectious Diseases. Organisms that are 

 strictly parasitic and therefore cannot grow apart from the human 

 body must, in order to produce disease in a second person, be 

 transferred from one person to another by direct contact; the 

 leprosy bacillus may be taken as an example. Diseases produced 

 by these organisms are said to be contagious. Other organisms 

 not so strictly parasitic, which are able to adapt themselves to 

 other conditions outside of the body, may gain access to a second 

 individual by means of contaminated material. A disease thus 

 produced is spoken of as infectious. No strict rule, however, 

 can be adhered to in such a classification since bacteria commonly 



