THE BIOLOGY OF BACTERIA 



31 



(which is never so injurious to organisms as moist heat ) ' : 

 {a) the Bunsen burner, in the flame of which platinum 

 needles, etc., are steriHsed ; {p) hot-air chamber, in which 

 flasks and test-tubes are heated to a temperature of 150-170° 

 C. for half an hour. For moist 

 heat : [c] boiling, for knives and in- 

 struments ; {d^ Koch's steam steri- 

 liser, by means of which a crate is 

 slung in a metal cylinder, at the 

 bottom of which the water is 

 boiled ; {e) the autoclave, which is 

 the most rapid and effective of all 

 the methods. This is in reality a 

 Koch steriliser, but with apparatus 

 for obtaining high pressure. The 

 last two id, e) are used for sterilis- 

 ing the nutriment media upon 

 which bacteria are cultivated out- 

 side the body. Blood serum 

 would, however, coagulate at a 

 temperature over 60° C. (124° F.^ 

 and hence a special steriliser has 

 been designed to carry out frac- 

 tional sterilisation daily for a week 

 at about 55° 0.-58° C. 



The Associatiofi of Organisms, 

 At a later stage we shall have an 

 opportunity of discussing symbi- 

 osis and allied conditions. Here 

 it is only necessary to draw attention to a fact that is rapidly 



^ It will be observed that there is a marked difference between the effects of 

 dry heat and moist heat. Moist heat is able to kill organisms much more readily 

 than dry, owing to its penetrating effect on the capsule of the bacillus. Dry 

 heat at 140'' C. (284'' F.), maintained for three hours, is necessary to kill the 

 resistant spores of Bacillus anthracis and B, subtilis, but moist heat at fifty 

 degrees less will have the same effect. It is from data such as these that in 



Koch's Steam Steriliser 



