PHYSIOLOGY OF THE MICROBES 89 



that Pasteur explained the immunity of the body by the 

 exhaustion of the food material which it supplies to the 

 microbe. 



Exhaustion of the food-stuffs and action of the excreta may 

 exist together. For example, when gelatine is inoculated 

 with fi millions of bacillus coli per milligram of medium 

 no growth takes place; the bacteria die and disintegrate 

 although the medium is not exhausted. 



Further, an "exhausted" medium can be regenerated by 

 filtering it through porcelain and heating it without adding 

 any new food material (Eijkman). In cultures of B. coli of 

 five days at 37° C, there is of all the bacteria which can be 

 seen and counted under the microscope, only one living in 

 fifteen, and after a week only one in forty (Hehewerth). 

 The antitoxin of one bacterial species can act on other 

 species. 



Heat Production. — The combustion of the food liberates 

 a quantity of energy which is not entirely used up in the 

 construction and support of the bacterial cells ; there remains 

 an excess of heat which raises the temperature of the medium. 

 The yeast of beer undergoing anrerobic fermentation heats 

 up the whole mass by 3" 9° C. (Eriksson). In heaps of 

 manure or hay, the temperature may rise to 50 or 70° C., 

 and in hay even to 96° C. Cohn found in the masses of 

 moist cotton a micrococcus which discharges carbonic acid 

 and raises the temperature to 67° C, when care is taken to 

 avoid loss of heat by radiation. 



But it is not very certain that the heating of hay is really 

 due to microbes. It is only the spores which can resist 

 temperatures bordering on 100° C., and spores exert no 

 activity. Further, no bacteria are to be found in the places 

 where the heating begins, and finally, hay sterilized at 1 20° C. 

 can heat like normal hay. 



According to Boekhout and Ott de Vries, the spontaneous 

 heating of hay is a chemical phenomenon, the cause of which 

 is still unknown. 



Production of Ligfht. — Rotting wood and the corpses 



