FACTORS INFLUENCING BACTERIA 63 



temperature of which is 15 '^ C. or even lower. In 1887 Forester 

 isolated from phosphorescent fish light-emitting bacteria which 

 not only lived at 0° C. but actually reproduced at this tempera- 

 ture. Since then numerous organisms have been isloated from 

 soil and salt waters which rapidly multiply at 0° C. or slightly 

 lower. To them has been given the name of fsychrofhilic or 

 cold-loving bacteria. These are of considerable importance in 

 soils of the northern climes and probably in the changes going 

 on in meats and vegetables while in cold storage. 



In contrast to these cold-loving bacteria are certain so-called 

 thermofhilic or heat-loving bacteria. These organisms have been 

 repeatedly obtained from the waters of hot springs, the interior 

 of fermenting manure and ensilage, soil, and the intestinal con- 

 tents of man and animals. Some of them multiply at a tempera- 

 ture of from 70° to 80^ C. What an interesting speck of living 

 matter that can live and function at such a temperature! Are 

 they similar to the host of the infernal regions? For this is near 

 the boiling point,— this temperature rapidly coagulates egg al- 

 bumen, produces painful burns on the skin, and quickly kills 

 most microbes. 



Between the cold-loving and heat-loving species is the class 

 which contains the overwhelming majority of microbes — the me- 

 sofhilic organisms. These may be divided into two great classes — 

 those found in the body of man and animals during health and 

 disease which have an optimum temperature of about blood-heat 

 (37.5^ C), and those whose optimum temperature is usually be- 

 tween 20^ and 35° C. To this last belong all the beneficial 

 soil organisms. 



The minimum temperature is the lowest at which bacterial 

 growth will occur. With many of the disease-producing organ- 

 isms it is only two or three degres below the temperature of the 

 body of the animal in which the microorganisms are usually 

 found. For some heat-loving bacteria it is as high as 40° C. 

 and for the cold-loving as low as 0° C. or below. The maxi- 

 mum temperature is the highest at which growth and multiplica- 

 tion can take place. This in the case of the pathogenes is only 



