CHEMICAL CHANGES WROUGHT BY BACTERIA 35 



as food in such a form that the animals can use them 

 for their cell needs. It is not the purpose of this book 

 to dwell upon this abstract matter of general biology, 

 but the principles of the activities of non-pathogenic 

 bacteria can well be seen in those inhabiting the 

 intestines. 



It may be possible for a human being to live without 

 bacteria in the alimentary tract, but some of those 

 present are beneficial in effect. A perfectly healthy 

 young animal may be born without bacteria in the 

 intestines, but organisms soon gain entrance with 

 air and food, since practically no object in the world 

 of life is free of them. The ordinary saprophytes of 

 the intestinal tract assist in making fats more easily 

 assimilable, and destroy some of the pathogenic 

 bacteria. 



Bacteria require for their life moisture, some degree 

 of heat, and a variety of foodstuffs. 



The amount of moisture is of little importance pro- 

 vided sufficient is available to make up the physical 

 bulk of the organism and assist in the passage of food- 

 stuffs through the cell wall. The substances used by 

 bacteria in nutrition are dissolved or suspended in 

 water. Temperature requirements are, however, more 

 exact, and every class has its own preferred degree. 

 Those which commonly inhabit the animal body 

 require a temperature of 98 F. (37 C.), while those 

 living naturally in soil or water thrive best at 60 to 

 70 F. (15 -21 C.) . Foodstuffs must contain the same 

 substances as for the growth of other plants, but the 

 organisms which infest the animal body, grow most 

 luxuriantly when animal tissue or fluid is present. 



