RELATION TO ENVIRONMENT CLASSIFICATION 37 



described certain phosphorescent bacteria, isolated from sea-water, 

 which grow readily at C., or a little above. On the other hand, 

 Miquel 25 has described non-motile bacilli, which he isolated from the 

 water of the Seine, which grew rapidly at temperatures ranging 

 apout 70 C., and the so-called "mucedinees thermophiles, " de- 

 scribed by Tsiklinski, 26 develop most readily at temperatures very 

 little above this. It is thus plain that the temperatures favored by 

 various bacteria depend to a large extent upon an adaption of these 

 bacteria through many generations to specific environmental condi- 

 tions. A good illustration of this is furnished by the bacillus of 

 avian tuberculosis, a microorganism differing essentially from the 

 bacillus of human tuberculosis in that its optimum growth tempera- 

 ture lies at 41-42 C., a temperature which exceeds the optimum 

 temperature for the human type by as much as the normal tempera- 

 ture of birds exceeds that of man. The same principle is illustrated 

 by the facts that the bacteria which have a very low optimum tem- 

 perature are usually those isolated from water, and the so-called 

 thermophile or high-temperature bacteria are obtained from hot 

 springs and from the upper layers of the soil, where, according to 

 Globig, 27 occasionally temperatures ranging from about 55 C. occur. 



As stated before, one and the same species may develop within a 

 wide temperature range, and it may be possible, by persistent culti- 

 vation at special temperatures, to adapt certain bacteria to grow lux- 

 uriantly at temperatures removed by several degrees from their 

 normal optimum. In such cases it may often occur that special 

 characteristics of the given species may be lost. An example of this 

 is the loss of virulence and of spore-formation which takes place 

 when anthrax bacilli are cultivated at 42 C., or the loss of the power 

 to produce pigment when bacillus prodigiosus is grown at tempera- 

 tures above 30 C. 



The vegetative forms of most of the pathogenic bacteria may 

 grow at temperatures ranging between 20 and 40 C. This can, 

 however, by no means be regarded as applicable to all of the patho- 

 genic bacteria, as some of these, like the gonococcus, the pneumo- 

 coccus, the tubercle bacillus, and others, are delicately susceptible to 

 temperature changes and have the power of growing only within 



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

 28 TsiTdinski, Ann. Past., 1889. 

 27 Globig, Zeit. f. Hyg., iii. 



