128 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



plants and animals. In these forms it has been found 

 possible to extract by suitable methods from the phos- 

 phorescent organs, two substances which when mixed will 

 cause a solution to glow. The light developed is rather 

 yellowish-green in color. When these organisms occur in 

 great numbers, as they may occasionally in sea water, they 

 may be the cause of diffused phosphorescence. They 

 sometimes produce luminescence on decaying fish that have 

 been thrown up by the waves on the seashore. 



PRODUCTION OF HEAT 



Microorganisms in general secure their energy for de- 

 velopment and growth by oxidative processes. In most 

 instances some of the energy secured is released in the form 

 of heat. Such heat production may be studied by use of 

 Dewar flasks, which are especially designed to conserve 

 heat and prevent its radiation. By this use it is usually 

 possible to measure the amount of heat developed by vari- 

 ous fermenting materials, such as by yeast in cane sugar, 

 or by bacteria in the souring of milk. The latter phenome- 

 non has been studied by Hill (1911). This author found 

 that in a little less than twenty-four hours the bacteria 

 produced approximately one and three-tenths calories of 

 heat per gram of milk, during the process of souring. 



Bacteria in nature sometimes produce appreciable in- 

 creases in temperature where there is opportunity for 

 oxidation, and the heat is not rapidly radiated. Loosely 

 piled manure, for example, or damp straw will heat, the 

 temperature rising in some cases to 60 or 70 C. The fact 

 that heat is gradually given off during the process of 

 decomposition is made use of by the market gardeners in 

 the preparation of hot beds. The amount of heat given 

 off by the manure used is sufficient to raise appreciably the 

 temperature under the glass frame. Loosely packed ensi- 

 lage may also show some rise in temperature, and frequently 



