STUDIES OF SPOBE-PLANTS 289 



probable that only in this way can their secretions be abun- 

 dant enough to check other bacteria in the intestines. 



(c) Bacteria in Butter and Cheese. The peculiar flavors of 

 butter and cheese are due to certain species of bacteria, and 

 hence the scientific dairyman gives special attention to 

 methods which will prevent the growth of undesirable species 

 and favor the desirable ones. By using pure cultures of 

 bacteria (and sometimes certain molds), it is possible to pro- 

 duce the desired quality of butter and cheese. The dis- 

 agreeable flavor of butter made in many farm-houses is due 

 to undesirable bacteria. See Conn's " Bacteria, Yeasts, 

 and Molds " ; and pamphlets of the United States Depart- 

 ment of Agriculture on butter and cheese making. 



(d) Bacteria in Vinegar. The change of alcohol into 

 vinegar by bacteria has been mentioned in connection with 

 yeast. " Mother-of- vinegar " is a mass of bacteria imbedded 

 in a gelatinous substance which they secrete. 



(e) Bacteria and Textile Fibers. Many fibers, such as those 

 of flax, hemp, and others obtained from the stems of plants, 

 are obtained by rotting the stems until the surrounding 

 tissues are soft. Bacteria do this work. 



(/) Useful Decomposition. While the action of bacteria 

 in decomposing foods prepared for human use is harmful 

 and financially a source of great loss, we should not forget 

 that this same process of decomposition is absolutely neces- 

 sary in order to keep up the cycle of organic matter ( 116, 

 117). We repeat for emphasis the statement made elsewhere 

 that but for the decomposing action of bacteria, aided by 

 other micro-organisms, the world would soon be so filled 

 with dead bodies of animals and plants that the carbon and 

 nitrogen available in the food-supply of living things would 

 be bound up in dead organic matter. Hence as decomposers 

 of organic jnatter the bacteria are indispensable. 



A splendid example of the usefulness of bacteria in causing 

 decomposition is found in the latest methods for disposal of 



