98 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



it is possible to make an observation practically every 30 minutes. 

 The course of the metabolism after the taking of the food can thus be 

 closely followed and a satisfactory curve obtained showing the imme- 

 diate effect, the maximum increment, and the gradual cessation of the 

 excess heat production. The short-period method is thus more espe- 

 cially fitted for studying small variations in metabolism and particu- 

 larly the rapidly occurring and disappearing changes. 



Although sufficient material is obtained by this method of measure- 

 ment to draw a graphic picture of the metabolism, the conditions are 

 still not ideal, as the measurements are not continuous and small varia- 

 tions and possible compensation may thus be lost, especially if the 

 intervals between periods are lengthened from any cause. 



This method of determining the metabolism for comparison purposes 

 is further open to criticism in that the assumption must be made that 

 the metabolism remains constant throughout the experimental day, 

 whereas the results may be affected by a daily rhythm or variation. 

 The question may be fairly asked : When no food is taken, is the metab- 

 olism the same at 3 p. m. as at 9 a. m.? In other words, if a base-line 

 is determined at 9 a. m., food is given at 10 a. m., and the influence of 

 the food is followed until 3 or 4 p. m., can it be assumed that the incre- 

 ment noted at 4 p. m. above the base-line found at 9 a. m. is due exclu- 

 sively to the influence of food, or is it due in part to a daily rhythm? 

 Johansson found in his experiments, which were carried out with pre- 

 cautions to maintain absolute muscular repose, that the time of day 

 had but little or no influence upon the carbon-dioxide excretion. 1 In 

 considering the results of our experiments made by the short-period 

 method, this question of constancy in the basal metabolism from hour 

 to hour may be discussed intelligently, for a large amount of data is 

 available from which conclusions may be drawn. 



DISCUSSION OF RESULTS OF SHORT-PERIOD EXPERIMENTS. 



Aside from a few experiments in which the Tissot apparatus was 

 used, 2 the universal respiration apparatus 3 was employed exclusively 

 for the short-period experiments. The experiments usually began 

 between 8 and 9 a. m. and continued until noon, and sometimes later; 

 the periods as a rule varied but little from 15 minutes in length. In 

 some instances the experiment was 18 periods in length, but the ma- 

 jority were from 5 to 6 periods long. 



The data for all of the subjects with whom experiments of five or 

 more periods have been made have been collected and tabulated; the 



Johansson, Skand. Arch. f. Physiol., 1898, 8, p. 103. Magnus-Levy likewise states that the 

 time of day has no influence upon the metabolism. (Magnus-Levy, Arch. f. d. ges. Physiol., 

 1894, 55, p. 32.) 



2 Tissot, Journ. de physiol. et de pathol. gen., 1904, 6, p. 688. 



'Benedict, Am. Journ. Physiol., 1909, 24, p. 345; Deutsch. Arch. f. klin. Med., 1912, 107, p. 156. 

 See, also, p. 202 of this monograph. 



