Physiological Efficiency 123 



Climatic conditions and the methods of construction of 

 filter beds are, therefore, important in so far as they 

 affect the numbers and physiological efficiency of the 

 bacteria. 



It will be readily perceived, then, that in tropical 

 and sub-tropical countries, the work of bacterial decom- 

 position is intensified by the more rapid multiplication 

 of the organisms. Furthermore, conditions favorable 

 for the rapid multiplication of bacteria are also favorable 

 for the development of a high degree of physiological 

 efficiency. On the other hand, cold weather retards the 

 multiplication of the organisms and also reacts unfavor- 

 ably on their physiological efficiency. As an illustration 

 of this are the observations made in Massachusetts in 

 the year following the very severe winter of 1903-1904. 

 When cold weather set in, the filters showed a marked 

 faUing off in their efficiency and did not fully recover 

 during the following year. 



Factory wastes and bacterial efficiency. — The numbers 

 and physiological efficiency of the organisms may be 

 affected by factors other than temperature and aeration. 

 In industrial centers where the factory wastes are added 

 to the sewage, a favorable effect may be exerted on the 

 sewage bacteria in occasional cases. More frequently, 

 however, such factory wastes are decidedly injurious, 

 and may seriously interfere with the proper working of 

 the bacterial filters. 



The use of acids in many industrial processes leads 

 to the production of acid sewage. When thie volume of 

 such sewage forms a considerable proportion of the 

 total, the bacteria which are very sensitive to even a 



