TEMPERATURE AND LIFE. 419 



or functions, and it may be said that for all life there is a degree of 

 temperature which is more favorable than any other to its perfect 

 development. The limits of temperature thus favorable to a given 

 class are surprisingly narrow. This is especially true in the case of 

 microbes. The bacillus of butyric fermentation is most active at 40o. 

 At 42^" it multiplies more rapidly, but diminishes in activity. At 45^ 

 it no longer effects fermentation. For alcoholic fermentation the most 

 favorable point is between 25° and 30°, although it ceases at zero — the 

 freezing point, and at 100o~the boiling point. The microbe of car- 

 buncular diseases thrives at 37° to 30°. At 41° it dies. Convincing 

 evidence of this is given by Pasteur, who has shown that a fowl in 

 normal condition, its temperature being from 41° to 42°, can not become 

 inoculated with a disease of this kind. If you cool the fowl artificially 

 by means of cold water, so that its temperature diminishes 2° or 3°, 

 the microbe multiplies abundantly in the blood of the fowl and 

 kills it, at least if the cooling process is continued. If that ceases, a 

 return to the normal condition of the animal will dissipate the disease. 

 A temperature of 35° is most favorable to lactic fermentation. The 

 fermentation of putrid matter is less restricted. It is carried on any- 

 where from 0° to 40°, although the most favorable points are between 

 15° and 35°. Examples of this kind may be given in great numbers. 

 What is more interesting, however, than this enumeration, is the study 

 of the results which are induced by subjecting a given microbe to a 

 degree of temperature higher than that which is best adapted to it, not 

 sufficiently high, however, to be fatal to its existence. Very evident 

 modifications are by this means produced in its physical condition. It 

 becomes weakened, and there is a marked diminution in its vitality. 

 This fact is the basis of the interesting processes of preventive vaccina- 

 tions, of which Pasteur has given us so many striking and useful exam- 

 ples. Only a slight increase of temperature is needed to transform a 

 dangerous microbe into an invaluable auxiliary in the art of healing or 

 preventing infectious diseases. On the contrary spores of bacteria can 

 be subjected to considerable variations of temperature without being 

 productive of any modifications. These spores withstand admirably 

 extremes of temperature, for instance —100° and -|-100°, the bacteria 

 which spring from these losing none of their virulence. Some species 

 of bacteria may be frozen for many months and live. This is true of 

 the bacteria of typhoid fever, according to Fraenkel and Prudden. 

 Contrary to the general impression, congealing does not purify impure 

 water. 



It is interesting to note that the sensibility of common leavens, as 

 referred to their thermic variations, is repeated in soluble leavens — 

 that is to say, with the products of the activity of certain cellules, which 

 exhibit some of the qualities of the ordinar}^ leavens. Thus pepsin is 

 active anywhere between 37° and 40°. At 50° it acts in a less degree, 

 becoming almost inactive at 90°. The pancreatic juice exercises its 



