PRODUCTS OF METABOLISM 187 



is probably much simpler because phosphorus does not enter as easily 

 into organic compounds as nitrogen. 



Physical Products of Metabolism 



Productiqn or Heat. — It has long been known that fermentation 

 prodvfces heat. The rise of temperature is usually not very great. In 

 lactic fermentation it amounts to about 1°, in alcoholic fermentation to 

 2 or 3°, but in certain processes the heat Uberated is considerable, as 

 in the fermentation of manure, of ensilage, of vinegar, and in others. 



The cause of heat formation is quite evident from the discussion on 

 page 142. Decomposition of organic matter means a liberation of 

 ener'gy which is used for the continuation of Ufe processes; the utiliza- 

 tion is, as a rule, incomplete, and a part of the energy appears in the 

 form of heat. The amount of heat produced can be measured directly 

 with the thermometer if great care is taken that no heat is lost by 

 radiation or by evaporation of water. 



Much heat is produced in the vinegar fermentation. In the quick- 

 vinegar process (page 546) the temperature rises sometimes as high as 

 10° to 15° above the temperature of the room and the vinegar manu- 

 facturer uses the heat produced by the bacteria to keep the generators 

 at the optimum temperature. If the process is not controlled carefully, 

 the vinegar bacteria are hkely to produce sufficient heat to kill 

 themselves. 



The heat produced in the fermentation of manure, especially horse 

 maiture, is used in the hot-beds to cultivate and force young plants. 

 In the manure pile, great heat production is not desirable because high 

 temperatures will volatilize the ammonia; the tight packing of manure 

 which keeps out the oxygen will prevent too strong bacterial action. 

 The highest temperature in silos which has been recorded is about 70°, 

 but the best silage is secured by keeping the temperature below 50°. 

 Ensilage fermentation is not thoroughly understood, however, and no 

 accurate statements can be made as to the cause of the increase in 

 temperature. Sometimes the temperature in silos does not exceed 

 35°. The curing of hay is usually accompanied by a rise of temperature. 

 For some time it was beUeved that the spontaneous combustion of hay 

 was mainly due to microorganisms, but it has been shown recently 

 that even sterile hay will show a rise of temperature under certain 



