RESPIRATION AND FERMENTATION 255 



the respiratory coefficient, the higher is the heat liberation during 



combustion, and vice versa. Proteins and fats exhibit therefore 



a high heat equivalent, organic acids a low one. 



Variations in the heat equivalent in dependence on the food 



material supplied may be most readily observed in molds which 



possess scarcely any reserve substances of their own, but are 



endowed with a very high intensity of respiration. When such 



CO- 

 fungi are grown on carbohydrates, the — — ratio is almost equal to 



O2 



1; when cultivated on fats, it falls to 0.7; and on acids, it rises to 

 2 to 3. But if these organisms are supplied with a mixture of 

 sugar and other substances, the coefficient will be at first close to 1, 

 until the sugar is spent. Then the combustion of the other sub- 

 stances will begin with a consequent change in the ratio. It is 

 interesting to note that even in oily seeds the coefficient may be 

 increased until it approaches 1, if sugar is supplied from without. 

 This shows clearly that sugar is the chief respiratory material. 

 Kostytschev is even of the opinion that sugar is the only directly 

 combustible material, the other substances, such as proteins 

 and fats, undergoing transformation into sugar previous to com- 

 bustion. 



The predominant role of the sugars in nutrition, as well as in 

 respiration, is moreover suggested by the interesting fact that 

 molds develop considerably slower on fats than on sugars. The 

 reason of this is that fats must previously undergo a complex 

 transformation, while sugars are utilized directly. The same is 

 indicated by the transformation of fats into sugars during the ger- 

 mination of oily seeds (Art. 69). 



79. Respiration at the Expense of Mineral Substances. 

 Nitrification, Sulphur and Iron Bacteria. — The general rule of 

 preference of sugar in respiration to all other materials does not 

 apply to certain groups of bacteria using inorganic substances for 

 respiration. In these bacteria one finds a peculiar process of 

 carbon assimilation, which proceeds not at the expense of the 

 radiant energy but as a result of the oxidation energy of such 

 substances as ammonia, hydrogen sulphide, etc. This is a process 

 of chemical synthesis (Art. 8). Here belong in the first place the 

 nitrification bacteria, which live in the soil and convert ammonia, 

 formed by the decomposition of organic refuse, into salts of nitrous 

 and nitric acid. 



