172 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



It is surprising, however, that according to the method of com- 

 puting the energy used by Rubner at that time, it was assumed that 

 the carbohydrates were first burned. As the 600 grams of cane sugar 

 given on that day correspond to an energy consumption of approxi- 

 mately 2,400 calories, or more than was actually measured, it is pre- 

 sumable that the 2, 023 calories given by Rubner as the value for the heat 

 output is based upon the assumption that the combustion for the day 

 was entirely of pure carbohydrate. This amount of energy would be 

 produced by the combustion of approximately 510 grams of sugar. 

 It is well known that 50 to 100 or more grams of glycogen may be with- 

 drawn on the first day of fasting. It is quite likely, therefore, that an 

 appreciable portion of the sugar ingested may have been used to form 

 glycogen and not to contribute to the increased metabolism measured 

 by Rubner. 



Rubner's calculations are seriously hampered by the absence of data 

 regarding the oxygen consumption, which would contribute more 

 directly to the computation of the total energy transformations. The 

 increment in the carbon-dioxide production has been more employed 

 for such researches as these than any other factor. Even when used 

 in special studies like those of Johansson and Gigon, 1 an attempt to 

 explain the processes on the basis of this increment immediately results 

 in great confusion. A typical case will serve to illustrate this. 



If a subject has been without food for 12 hours or more and is drawing 

 upon body material to the extent of 15 per cent of the total energy in 

 the form of protein and the other 85 per cent is apportioned between 

 carbohydrate and fat, presumably in the proportion of 45 per cent 

 of carbohydrate and 40 per cent of fat, the respiratory quotient will 

 be approximately 0.85. When carbohydrate is ingested there is 

 immediately a great rise in the respiratory quotient and an increase in 

 the production of carbon dioxide. It may be argued, then, in common 

 with the old conception of von Hoesslin, 2 that a fat-carbohydrate- 

 protein combustion is replaced by an exclusively protein-carbohydrate 

 combustion, without altering in any way the total amount of energy 

 transformed. This is one possibility. 



Another possibility is that there may be a transformation of carbo- 

 hydrate into fat. By this process, which has been definitely proved in 

 several laboratories in a number of ways, there may be a formation of 



'Probably no research on the influence of the ingestion of pure carbohydrate has been more 

 accurately and carefully carried out than that of Johansson at Stockholm (see pp. 34 and 35), which 

 was supplemented by the subsequent experiments of Johansson's former assistant, Gigon (see p. 38) . 

 While Rubner's criticism (Die Gesetze des Energieverbrauchs bei der Ernahrung, 1902, p. 216) 

 of Johansson's method of computing the carbon-dioxide production of a single individual in half- 

 hour periods seems justified when we consider that the volume of air in the chamber was 100,000 

 liters, nevertheless personal visits to Stockholm have convinced us that the remarkable Sonden 

 gas-analysis apparatus used by Johansson permits measurements of carbon dioxide with a suffi- 

 cient degree of accuracy to justify recording values for half-hour periods with this chamber, if 

 not, indeed, for 15-minute periods. 



*von Hoesslin, Arch. f. path. Anat. u. Physiol., 1882, 89, p. 341. 



