PHYSIOLOGY OF THE MICROBES 95 



from air at 35-40 C, and can thus remain alive in the intestine 

 of animals. 



The majority of non-sporulating bacteria are killed in a few 

 minutes at a temperature in the vicinity of 60 C. Further, the 

 nature of the medium in which they are heated must be 

 reckoned with ; they perish more quickly in acid than in alkaline 

 fluids, and dry heat kills them much less quickly than moist. 

 The spores, being resistant forms, are only killed at much 

 higher temperatures : 100 C., during 2-4 minutes for the 

 anthrax spore. In one single species, there are spores which 

 stand the same temperature twice as long as their companions. 

 At higher temperatures resistance is much shorter, for example 

 for certain sporulating bacteria of the soil and of hay (in 

 saturated steam) : 



100 resistance ... . 16 hours. 



115 .~ ihour. 



130 . 5 minutes. 



140 ,, ... scarcely I minute. 



The spores of moulds, studied for the first time by 

 Spallanzani, stand thirty minutes of dry heat at 127-132 C., 

 but in moist surroundings they die below 100 C. The 

 spores of Ustilago carlo in the presence of saturated water 

 vapour perish at about 60 C. ; dry, they stand i2oC. Spores 

 are more resistant than the bacilli, because they contain less 

 water, e.g., 38 per cent, instead of 62 per cent. Tyndall's 

 method discontinuous heating, at intervals, about one hour 

 per day for three days in succession succeeds at a relatively 

 low temperature because the protoplasm in taking up water 

 becomes more vulnerable. 



Heating coagulates the protoplasm, and this coagulation is 

 the more rapid and easy the more water the protoplasm 

 contains. Albumin dried in vacua over sulphuric acid can 

 be heated beyond 100 without losing its solubility in water 

 (Chevreul). Since coagulation is not an instantaneous but a 

 progressive phenomenon, instead of talking of the " tempera- 

 ture of coagulation " and the " lethal temperature " it would 



