94 MICROBES AND TOXINS 



Action of Heat on Microbes. — Just as on ordinary 

 thermometers the temperatures are marked for taking a bath 

 or for keeping silk-worms, so it would be possible to mark the 

 points at which microbes develop best. Each species has an 

 optimum temperature; below this, it grows feebly; above it, 

 it begins to suifer and dies ; heat, indeed, is the sovereign 

 disinfectant. Adapted as they are to the surroundings which 

 shelter and nourish them, the bacteria are parasites, not only 

 in regard to their food supply, but also for their heat 

 surroundings. 



Although the names of different species might thus be written 

 on almost every degree of the thermometer, three types may be 

 distinguished, with intermediate individuals. The majority of 

 the bacteria of water and of soil and the phosphorescent 

 bacteria of fish grow well at 15 — 20° C. 



The majority of pathogenic microbes demand in cultures 

 the same temperature as that of the body in which they lived 

 as parasites. The tubercle bacillus of the mammals develops 

 best at 38° C. ; that of birds at 41-42°, and that of fishes at 

 15-20° C., i.e., practically like a water-bacterium. 



The third group is that of the thermophilic bacteria. They 

 demand and support temperatures so high that other bacteria 

 would rapidly be killed. They have been found in rivers, in 

 sewage, in cheese and in the human intestine. The majority 

 are motile and possess spores. In the hot springs of Ischia, 

 and in the fumaroles of Naples there are bacteria which live at 

 60° C. Miquel found in the Seine a species living best at 67° 

 to 70° C. In a spring at Luchon, Certes and Garrigou found 

 a bacterium developing at 64° C, the temperature of the water. 

 In the upper layers of the soil, Globig discovered species 

 which grow well at 65-70°. Mile. Tsiklinsky has studied the 

 thermophilic bacteria of the human intestine ; they are all 

 aerobes. 



It is remarkable that thermophilic species from the 

 surface of the soil have been found in the most varied 

 latitudes, from the tropics to the Hebrides and Norway 

 Perhaps those of the cold countries (rare) can live shut off 



