48 /'. / THOGENIC BACTERIA. 



Rarely, the presence of one species of microorganism 

 entirely eradicates another species. Hankin found that 

 tlu- Micrococcns Ghadialli destroyed the typhoid and colon 

 bacilli, and suggested the use of this coccus to purify 

 waters polluted with typhoid. 1 



(/) 7i in/>t rat itre. The question of temperature is of 

 importance from its bearing upon sterilization. Accord- 

 ing to Frankel, bacteria will scarcely grow at all below 

 1 6 and above 40 C. 



The researches of Fliigge show that the Bacillus sub- 

 tilis will grow very slowly at 6 C., and as the tempera- 

 ture is elevated it is said that until 12.5 C. is reached 

 fission does not occur oftener than every four or five 

 hours. When 25 C. is reached the fission occurs every 

 three-quarters of an hour, and at 30 C. about every half 

 hour. 



Most bacteria die at a higher temperature than 60- 

 75 C. The spores can resist boiling water, but are 

 killed by dry heat if exposed to 150 C. for an hour or to 

 175 C. for five to ten minutes. Freezing kills many, but 

 not all bacteria, but does not affect the spores at all. 



Most bacteria grow best at the ordinary temperature of 

 a comfortably heated room, and are not affected by its 

 -ional slight changes. Some, chiefly the pathogenic 

 forms, are not cultivable except at the temperature of 

 the animal body (37 C.); others, like the tubercle bacil- 

 lus, grow best at a temperature a little above that of the 

 body 40 C. 



Variations in the amount of oxygen, temperature, moist- 

 ure, etc., beyond what have been described, are prej- 

 udicial to the growth and development of bacteria, first 

 inhibiting their growth, thus tending toward their de- 

 struction. In the practical application of our knowledge 

 of the biology of the bacteria we constantly make use of 

 such precautions as removing from surgical dressings, 

 sponges, etc., every substance that can possibly afford 

 nutriment to bacteria, and heating such materials, as well 



'/. Jour., Aug. 14, 1897, p. 418. 



