890 METABOLISM. 



and which permits the estimation of the nitrogen of the urine and the carbon 

 dioxide expired, as well as the inspired oxygen and the quantity of heat produced. 

 If we start from the theoretically calculated formulae for the various possible 

 transformations of the proteins, fats, and carbohydrates in the body, it is clear 

 that other values must be obtained for the heat, carbon dioxide, oxygen, and 

 nitrogen of the urine, when one, for example, admits of a complete combustion 

 of proteins to urea, carbon dioxide, and water, or of a partial splitting off of fat. 

 Another relation between heat, carbon dioxide, and oxygen is also to be expected 

 when the fat is completely burnt or when it is decomposed into sugar, carbon 

 dioxide, and water. In this way, by a comparison of the values found in special 

 cases with the figures calculated for the various transformations, KAUFMANN 

 attempts to explain the various decomposition processes in the body under dif- 

 ferent nutritive conditions. 



The organic foodstuffs serve in part to replace the necessary losses 

 of the organs and in part as sources of energy. Under all circumstances 

 a restitution of the protein-like constituents of the organs is necessary. 

 This replacement is, according to RUBNER, represented by the so-called 

 wear-and-tear quota (see below) which amounts to about 4-6 per cent of 

 the total energy transformed and which can be supplied by proteins only. 

 For the supply of the remaining exchange, which according to RUBNER 

 serves as source of energy, all three groups of organic foodstuffs can be 

 used, and investigations carried out by RUBNER have taught that these 

 foodstuffs can act as sources of energy in the animal body in a proportion 

 which corresponds with the respective figures of their heat value. This 

 is apparent from the following table. In this is found the weight of 

 the various foods equal to 100 grams of fat, a part determined from 

 experiments on animals and a part calculated from figures of the heat 

 values: 



From Experiments From the Difference, 



on Animals. Heat Value. per cent. 



Syntonin 225 213 +5.6 



Muscle-flesh (dried) .... 243 235 +4 . 3 



Starch 232 229 +1.3 



Cane-sugar 234 235 -0 



Glucose 256 255 -0 



From the given isodynamic value of the various foods it follows that 

 these substances replace one another in the body almost in exact ratio 

 to the energy contained in them. Thus in round numbers 227 grame of 

 protein and carbohydrate are equal to or isodynamic with 100 grams of 

 fat in regard to source of energy, because each yields 930 calories on com- 

 bustion in the oody. 



By means of recent very important calori metric investigations, RUB- 

 NER l has shown that the heat produced in an animal in several series of 

 experiments extending over forty-five days corresponded to within 0.47 

 per cent of the physiological heat of combustion calculated from the decom- 



Zeitschr. f. Biologic, 30. 



