COMBATING PARASITIC BACTKRlA. 169 



be immersed in liquids, and therefore their pas- 

 sage from individual to individual must be a pas- 

 sive one. They are readily transferred, however, 

 by a number of different means, and the study of 

 these means is aiding much in checking contagion 

 Study along this line has shown that the means 

 by which bacteria are carried are several. First 

 we may notice food as a distributor. Food may 

 become contaminated by infectious material in 

 many ways ; for example, by contact with sewage, 

 or with polluted water, or even with eating uten- 

 sils which have been used by patients. Water is 

 also likely to be contaminated with infectious 

 material, and is a fertile source for distributing 

 typhoid. and cholera. Milk may become contam- 

 inated in a variety of ways, and be a source of dis- 

 tributing the bacteria which produce typhoid 

 fever, tuberculosis, diphtheria, scarlet fever, and 

 a few other less common diseases. Again, in- 

 fected clothing, bedding, or eating utensils may 

 be taken from a patient and be used by another 

 individual without proper cleansing. Direct con- 

 tact, or contact with infected animals, furnishes 

 another method. Insects sometimes carry the 

 bacteria from person to person, and in some dis- 

 eases (tuberculosis, and perhaps scarlet fever and 

 smallpox) we must look to the air as a distribu- 

 tor of the infectious material. Knowledge of 

 these facts is helping. to account for multitudes 

 of mysterious cases of infection, especially when 

 we combine them with the known sources of con- 

 tagious matter. 



Means of Invasion. Bacteriology has shown us 

 that different species of parasitic bacteria have 

 different means of entering the body, and that 

 each must enter the proper place in order to get 



