18 APPLIED BACTERIOLOGY FOR NURSES 



genie bacteria) are only a small proportion of the bac- 

 teria thus far known. Many bacteria are very import- 

 ant in preparing food for plants, breaking down com- 

 plex chemic substances into simpler substances suitable 

 for plant absorption. Still other bacteria are useful in 

 producing fermentations, in disposing of refuse, liquefy- 

 ing sewage, etc. Bacteria are found almost every where- 

 in the air, in water, in the soil, and on everything we 

 touch. Most of the bacteria of the air, however, are 

 entirely harmless, although at one time it was believed 

 that they caused the infection of wounds during surgical 

 operations. Lister used to have a spray with dilute 

 carbolic acid playing about the operating room during 

 an operation in order to kill the bacteria which might 

 be in the air. We have since found out that this is 

 unnecessary. 



It was stated above that bacteria multiplied enor- 

 mously when placed under proper conditions. These con- 

 ditions relate mainly to food supply, to the presence of 

 a suitable temperature, sufficient moisture, absence of 

 much light, presence or absence of oxygen, etc. We 

 shall take up the points in the order named. In suj>- 

 plying living creatures with food, it is always well 

 to have the composition of this as nearly as possible like 

 that of their natural food. In the case of bacteria 

 pathogenic for man and animals it is obvious that the 

 food should have a composition resembling that of 

 the animal body. This is accomplished by making use 

 of broths, milk, blood-serum, and the like. The same 

 principle applies to the temperature at which the bac- 

 teria are cultivated. Just as certain tropical plants 

 require a different temperature to grow than do hardy 



