34 BIOLOGY AND TECHNIQUE 



Spirillum cholerse asiaticse 52 C. 



Diplococcus pneumonise 52 C. 



Streptococcus pyogenes 54 C. 



Bacillus typhosus 56 C. 



Bacillus pyocyaneus 56 C. 



Bacillus mucosus capsulatus 56 C. 



Bacillus prodigiosus 58 C. 



Staphylococcus pyogenes aureus 58 C. 



Gonococcus 60 C. 



Staphylococcus pyogenes albus 62 C. 



The bacillus tuberculosis, though not a spore bearer, seems to be slightly 

 more resistant to heat than other purely vegetative microorganisms. 

 Thus, according to Smith 1 and others, ten and twenty minutes' ex- 

 posure to a temperature of 70 C. is necessary to destroy tubercle bacilli 

 in a fluid medium. For the effectual destruction of spores by moist 

 heat, a temperature of 100 C., or boiling point, is usually necessary. 



Low temperatures are much less destructive than the high ones, and 

 are even in a number of cases useful in keeping bacteria alive for long 

 periods, inasmuch as metabolic processes are inhibited and life is main- 

 tained without actual development in a sort of resting state. Actual 

 destruction by low temperatures rarely takes place. The exposure of 

 diphtheria, typhoid, and other bacilli to temperatures as low as 200 C. 

 below zero has been carried out without destruction of the microorgan- 

 isms, a fact which is of great importance in considerng the possibility 

 of infection by the vehicle of ice. Meningococci and gonococci, on the 

 other hand, die out rapidly when exposed to C. 



Relation to Pressure. High pressure does not injure bacteria. 

 Certes 2 found that a pressure of two atmospheres had no influence 

 upon the growth of anthrax bacilli suspended in blood. 



Relation to Moisture. For the growth and development of all bac- 

 teria, the presence of water is necessary. Nutritive materials can not 

 be absorbed by an osmotic process unless in a state of solution. While 

 complete dryness does not permit growth, its destructive action upon 

 various bacteria is subject to great differences. The effect of complete 

 drying upon bacteria will be found more fully discussed on page 62. In 

 the same place may be found a discussion of the effects of light, elec- 

 tricity, x-ray, and radium rays upon bacteria. 



1 Th. Smith, Jour, of Experimental Med., No. 3, 1899. 



2 Certes, Compt. rend, de 1'acad. d. sc., 99, Paris, 1884. 



