BACTERIOLOGY. 49 



typhoid bacillus, on account of the danger of taking 

 them into our intestinal tracts. Because cholera and 

 typhoid fever are most frequently contracted from the 

 drinking of polluted water, they are both spoken of as 

 ^^ water-home diseases. ^^ The same micro-organisms 

 are also common contaminators of other foods, the 

 source of the contamination, as a rule, being also 

 water, whether it be used to cleanse utensils, or a con- 

 taminated stream in which water-cress or oysters are 

 growing. 



The danger of air as a medium for the 

 Air. distribution of pathogenic bacteria has 



been much exaggerated, in fact, even the 

 number of all kinds of bacteria in the atmosphere is 

 not as great as is popularly supposed. True! they are 

 practically present everywhere, except at sea many 

 miles from shore, and at great altitudes; yet they are 

 never present in such abundance that ''it rains bacteria." 

 At one time the profession believed that the infectious 

 agents of many diseases were carried in the air even 

 considerable distances, a belief no longer held since the 

 importance of the role that insects play in the trans- 

 mission of disease has been recognized. 



The most widely distributed pathogenic micro- 

 organism in the air is the tubercle bacillus, the cause of 

 consumption, and a large variety of other ailments, 

 such as hip- joint disease, caries of the spine, etc. 

 Over 100,000 persons die annually from consumption 



