CHAPTER V 



CONDITIONS AFFECTING THE GROWTH OF BACTERIA 



The conditions that favorably or unfavorably- affect 

 the growth of bacteria, include temperature, moisture, 

 aeration, light, pressure, and the presence or absence 

 of injurious substances. The first of these (temperature) 

 is an important influence, since the living protoplasm 

 can perform its functions only within a comparatively 

 narrow range of heat and cold. Just as a few degrees 

 of temperature may hasten or retard the germination 

 of seeds, or the development of fruit-buds, so a similar 

 variation in temperature may increase or diminish 

 the intensity of bacterial development. There are 

 well-defined limits below or above which no bacterial 

 growth whatsoever will occur, yet within these limits 

 there are considerable variations among the different 

 species. Important differences as to suitable growing 

 temperatures occur between the soil and water bacteria, 

 on the one hand, and most of the disease bacteria in 

 warm-blooded animals, on the other. 



Thermophile bacteria. — There is a third class of bac- 

 teria, known as thermophile that are remarkable for 

 the high-temperature limits within which they will 

 grow. Thermophile bacteria have been isolated from 

 the soil and manure heaps, with the result that it has 



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