34 PHYSIOLOGY OF BACTERIA 



maintenance will ultimately be transformed into heat, and this 

 becomes evident by a temperature increase of the medium. 



In most fermentations, our customary methods of cultivation 

 show no increase of temperature because the heat of fermentation 

 is conducted and radiated away almost as fast as it is produced. 

 Even if we use thermos bottles, the increase of temperature rarely 

 exceeds 2°C. (see Figs. 1 and 2). Exceptions are only the oxidative 

 fermentations. In these, the temperature can rise very high if the 

 heat has a chance to accumulate. The heat produced from the oxida- 

 tion of alcohol by vinegar bacteria is sufficient to keep the tempera- 

 ture in the vinegar generators high, therefore care must be taken to 

 control the oxygen supply lest the temperature rise so high as to kill all 

 bacteria. This would correspond, biologically speaking, to death 

 by fever. Such temperature increases due to bacteria seem especially 

 high when we consider that less than 0.1% of the liquid is bacteria 

 bodies. 



Some bacteria produce light. This is another form in which energy 

 leaves the bacterial cell. The amounts of energy are very small 

 when compared with the amounts that leave the cells in the form of 

 heat. Ultraviolet radiation is claimed by Baron (1928) for several 

 yeasts and bacteria. 



The energy required by bacteria to move through a liquid has been 

 calculated by von Angerer (1919). He considers his estimates, 

 based on Stokes formula, only as very rough approximations which 

 give merely the order of magnitude. The calories required for one 

 hour's continuous swimming are calculated for one cell of V. cholerae 

 to be 216 X 10-16 cal., for Bact.'typhosum 10 X lO-^^ cal., for Bacillus 

 subtilis 25 X 10-^^ cal. The total energy liberated by one cell in 

 one hour (calculating from lactic acid fermentation) is of the order 

 of 10-1*^ calories. The energy required for motion is of the order of 

 10"^^ cal., and is negligible in comparison with the total energy 

 liberated. 



(e) SUMMARY 



The potential energy (combustion heat) of yeast and 

 bacteria cells is frequently similar to that of the food 

 from which they are made. Nevertheless, a considerable 

 amount of energy is required to produce these cells from 

 food. 



