CHAPTER X. 



1. HEAT DEVELOPMENT DUE TO BACTERIAL ACTIVITY: 

 THERMOGENIC AND THERMOPHILIC BACTERIA. 



As throughout the whole animal and vegetable world, respiration 

 results in a liberation of heat, so we shall expect the same to be true 

 for bacterial respiration : part of the energy derived by the breaking 

 down of food materials, or of the protoplasm, will be expended in the 

 development of heat. The experiments of investigators in this direc- 

 tion have shown the correctness of these deductions. If a culture of 

 bacteria be protected as far as possible from loss of heat by radiation, 

 conduction, etc., it shows a distinct rise of temperature, and exact 

 methods have been devised for estimating the amount of heat liberated. 

 In most cases of bacterial activity such a large amount of energy is 

 needed for purposes of growth, multiplication, etc., which involve an 

 absorption of energy, that much heat is not developed. Again, much 

 of the heat developed during respiration is dissipated by radiation and 

 conduction. Under certain conditions, however, some organisms 

 liberate a very large amount of energy in the form of heat, with the 

 result that a considerable rise in temperature takes place in the 

 medium in which these organisms are growing. In the preparation 

 of beer and wine the rise of temperature during fermentation is well 

 known. Again, a considerable development of heat always follows the 

 massing together of any humid mass of organic matter. We see 

 instances of this in the " smoking " of dung-heaps and in the disastrous 

 effect which follows the massing together of moist hay. In the fermen- 

 tation of the tobacco leaf the leaves are purposely moistened and then 

 massed together in large bundles in order to secure this rise of 

 temperature. Further instances are exhibited in the preparation, 

 for human consumption, of many of the products of nature, e.g. of 

 tea, coffee, cocoa, and many of the spices. 





