60 BACTERIOLOGY. 



inhibit for a time or destroy this property. Living bac- 

 teria are always found in phosphorescent cultures; a 

 filtered culture free from germs is invariably non-phos- 

 phorescent; but while the organism cannot emit light ex- 

 cept during life, it can live without emitting light, as in 

 an atmosphere of carbonic acid gas, for instance. Most 

 organisms require, in order to be able to emit light, the 

 presence of peptone and oxygen, and many also need 

 carbon and nitrogen. They are best grown under free 

 access of oxygen in a culture medium prepared by 

 boiling fish in sea- water (or water containing 3 per 

 cent, sea-salt), to which 1 per cent, peptone, 1 per 

 cent, glycerin, and 0.5 per cent, asparagin are added. 

 Even in this medium the power of emitting light is 

 soon lost unless the organism is constantly trans- 

 planted to fresh m^dia. 



Thermic Effects. The production of heat by bacteria 

 does not attract attention in our usual cultures because 

 of its slight amount, and even fermenting culture 

 liquids with abundance of bacteria cause no sensa- 

 tion of warmth when touched by the hand. Careful 

 tests, however, show that heat is produced. The 

 increase of temperature in organic substances when 

 stored in a moist condition, as tobacco, hay, manure, 

 etc., is one partly at least due to the action of bacteria. 

 Rabinowitsch suggests that very probably the high tem- 

 perature which is here exhibited is caused in part by the 

 so-called thermophilic bacteria, but there are no accurate 

 observations as to the true source of this heat. 



Chemical Effects. The processes which bodies being 

 split up undergo depend, first, on the chemical nature 

 of the bodies involved and the conditions under which 

 they exist, and, secondly, on the varieties of bacteria 



