BACTERIA IN THE INDUSTRIES 205 



the action which takes place and of the bacteria involved is very 

 incomplete. 



Bacteria are important factors in siloing; in curing tobacco, tea and 

 cacao. The flavor of different brands of tobacco is due to different bac- 

 teria, and attempts have been made to isolate those producing desirable 

 flavors and to use them in pure culture. It is highly probable that the 

 bouquet of old wines is due to bacterial action. These are, however, 

 matters which require further study. Rotting bacteria are active in 

 paper-making. In the maceration process certain bacteria feed upon and 

 decompose the less resisting vegetable cell-walls, as those of the paren- 

 chymatous tissues, the epidermal tissue, etc., leaving the more resisting 

 fibrous lignified tissues as bast and wood fibers. The pulp is then poured 

 on sieves and the rotted or digested portions washed out. 



Bacteria are now practically employed in the purification of sewage. 

 This is done in what are known as "contact beds," in which the environ- 

 ment is made favorable to rapid development of those non-pathogenic 

 rotting bacteria which disintegrate the organic substances and at the same 

 time prevent the development of the pathogenic or otherwise objectionable 

 microbes. It is highly probable that this method may be applied to the 

 purification of streams and other large bodies of water. 



The possibilities in the practical utilization of bacteria in the arts and 

 industries are promising, and it may confidently be expected that wonder- 

 ful innovations along this line will be made in the very near future. 



7. MICROBIOLOGICAL METHODS IN FOOD, MILK AND WATER 



ANALYSIS 



It is not the province of a work of this kind to enter into the discussion 

 of special methods of analysis. These must be gotten through other 

 sources and channels. The following practical methods are given for the 

 benefit of those who are endowed with sufficient inherent ability to apply 

 them. 



i. Water Analysis. Plankton Examination. V. Hensen applied the 

 term plankton to the minute organisms and other organic matter drifting 

 or floating in fresh and in salt water. The term therefore includes bac- 

 teria and other microorganisms, inclusive of dead organic matter and of 

 mineral matter. In the more limited sense plankton excludes bacteria; 

 although there is no satisfactory reason why this group should be ex- 

 cluded. The following methods have been used more or less. 



a. Hassell Specific Gravity Method. Let two or three liters of the 

 water to be examined stand in some suitable vessel for twelve to twenty- 

 four hours. Decant all but 200 cc. This remainder of 200 cc. with all 

 sediment, is poured into a conical test glass with rounded bottom and 



