32 BIOLOGY AND TECHJMiQUE 



temperature should intimately affect the metabolic processes. The 

 range of temperature at -which bacteria may grow is subject to wide 

 variations among different species. Each species, on the other hand, 

 may thrive within a more or less elastic range of temperature, each one 

 having an optimum, a minimum, and a definite maximum tempera- 

 ture. When the optimum temperature is present in the environment, 

 the functions of absorption and excretion keep pace with each other, and 

 the chemical balance is well preserved. When the temperature is lower 

 than the optimum, all metabolic processes take place more slowly, and 

 the bacterium gradually enters into a resting or latent stage, at which ac- 

 tual growth may be exceedingly slow or entirely inhibited. When the 

 temperature is higher than the optimum, the destructive processes are 

 carried on more rapidly than the substitution of waste products by ab- 

 sorption, and a gradual weakening of vital energy, or even a gradual 

 death of the bacteriutti, may take place. When certain bacteria form 

 spores, they become very much more resistant against both high and 

 low temperatures, probably because a true resting stage has been 

 reached, during which metabolism has been reduced to a minimum, 

 there being practically no nutritive material taken in and corresponding- 

 ly little destruction taking place within the body of the microorganism. 

 The optimum temperature for various bacteria depends upon the 

 habitual environment, in which the particular species is accustomed to 

 exist. Thus, for the large majority of bacteria pathogenic for human 

 beings, the optimum temperature is at or about 37.5° C. There are 

 a large number of bacteria common in water, however, which grow 

 hardly at all at the body temperature, but thrive most luxuriantly at 

 temperatures of about 20° C. F. Forster,' moreover, described certain 

 phosphorescent bacteria, isolated from sea-water, which grow readily at 

 0° C, or a little above. On the other hand, MiqueP has described non- 

 motile bacilli, which he isolated from the water of the Seine, which grew 

 rapidly at temperatures ranging about 70° C, and the so-called "muce- 

 dinees thermophiles," described by Tsiklinski,^ develop most readily at 

 temperatures very little above this. It is thus plain that the tempera- 

 tures favored by various bacteria depend to a large extent upon an 

 adaptation of these bacteria through many generations to specific en- 

 vironmental conditions. A good illustration of this is furnished by the 

 bacillus of avian tuberculosis, a microorganism differing essentially 



1 F. Farster, Cent. f. Bakt., ii, 1887. 



2 Miquel, Bull, de la Stat. Munic. de Paris, 1879. 



» TsihlinsU, Ann. Past., 1889. 



