716 DISTRIBUTION AND HABITAT OF THE BACTERIA. 



was there that Koch succeeded in demonstrating the 

 presence of cholera bacilli in one of the Indian tanks, and 

 proving that a marked saprophytic multiplication of the 

 bacilli had occurred on the banks of the tank. 



Eactena m We daily take into our bodies very large numbers of 



articles Of , . . , . , . . mm , n 



food. living bacteria, not only with water, but also with our 



food. To some articles of food for example, beer, 

 cheese, &c. numerous bacteria are intentionally added 

 in their preparation. In the case of other articles of 

 food, of which the edible portions are formed beneath 

 the surface of the soil, large numbers of bacteria adhere 

 to the particles of earth surrounding them. Others 

 again, such as fruits, are covered with numerous 

 bacteria from the air, which are either fixed on their 

 sticky surface, or are deposited there by the condensa- 

 tion of watery vapour. Further, it very frequently 

 happens that articles of food which were originally free 

 from bacteria, or which were sterilised in their prepara- 

 tion (milk, meat, various kinds of cooked food), are in- 

 fected either by contact or from the air, and according 

 to their nutrient conditions and the prevailing tem- 

 perature, smaller or larger colonies of bacteria develop 

 on them. 



In all these cases the colonies may consist of com- 

 pletely harmless saprophytes ; or, on the other hand, 

 bacteria may be present which are able to set up fer- 

 mentation, and which are not altogether indifferent, for 

 if taken into the body in very large numbers they may 

 exert their energies in too marked a manner in the 

 human digestive tract; or, again, the bacteria may 

 belong to a class which usually grow as saprophytes, 

 but which produce very active ptomaines, some of which 

 may cause morbid changes in the intestinal mucous 

 membrane; or, finally, pathogenic bacteria may be at 

 times present in the food. 



Development Those bacteria which develop on food kept in the 

 parasites on house seem to be especially worthy of attention. Under 

 food 1680 * these circumstances the temperature is often very 



