34 BIOLOGY AND TECHNIQUE 



mously increased. Exactly what the explanation of this is can not be at 

 present stated. It may be that the high concentration in which the 

 protoplasmic mass is found in the spores renders it less easily coagulable 

 than is the protoplasm of the vegetative body. A more detailed discus- 

 sionof these relations will be found in the section on Heat sterilization. 



The thermal death points of a large number of bacteria have been 

 very carefully studied by Sternberg/ by a special technique described 

 elsewhere. 



The thermal death points ascertained by him in this way, with an 

 exposure of ten minutes in a fluid mediiun, for some of the more common 

 non-sporogenic bacteria are as follows: 



Spirillum cholerae asiaticae 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° G. 



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 the researches of Smith ' and others, ten and twenty 

 minutes' exposure to a temperature of 70° C. is necessary to destroy 

 tubercle bacilU 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 

 maintained 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 microorganisms, a fact which is of great importance in considering 

 the possibility of infection by the vehicle of ice. Meningococci and 

 gonococci, on the other hand, die out rapidly when exposed to 0° C. 



' Sternberg, "Textbook of Bacteriology," New York, 1901. 

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



