INGESTION OF COFFEE. 



151 



superimposed upon the base-lines determined on the respective days. 

 The average heat production (computed) per minute, plotted for the 

 average time of the periods, supplied the points for defining the area of 

 increment. Inasmuch as this method was followed for all of the res- 

 piration experiments except the water-drinking and chewing studies, 

 it is described in detail here and two illustrative curves are given 

 (figures 1 and 2). 



The curve in figure 1 is that for the coffee experiment with L. E. E., 

 March 23, 1911. (See table 84.) The basal value for this day was 

 1.15 calories; the time between the drinking of 325 grams of coffee 

 and the end of the last period was 3 hours 50 minutes. The initial 

 value for this curve is on the base-line at the point indicated on the 

 horizontal scale as 0, this 

 being the time when the sub- 

 ject finished drinking the 

 coffee i. e., at 10 h 10 m a. m. 

 The point plotted 29 minutes 

 later is for 1.28 calories at the 

 average time of the first period, 

 that is, at 10 h 39 m a. m. 

 Values have been similarly 



130 



D 



..25 



a 

 o 



1.15 



1. 10 



Basal 



/\ 



value 



I iVi Z Z'/z 

 Hour* after food 



FIG. 1. Curve showing increment of heat production 

 following ingestion of 325 c.c. of coffee in experi- 

 ment with L. E. E., March 23, 1911. 



plotted at six other points 

 i. e.. 1.21 calories at 58 

 minutes, 1.28 calories at 1 

 hour 26 minutes, 1.29 calories 



at 1 hour 58 minutes, 1.28 calories at 2 hours 29 minutes, 1.26 cal- 

 ories at 3 hours 4 minutes, and 1.28 calories at 3 hours 43 minutes 

 after taking the coffee. The curve has been extended to reach a per- 

 pendicular dropped to the base-line at the point of time corresponding 

 to the end of the last period of the experiment. The area thus inclosed 

 by the curve and base-line is considered to represent the total incre- 

 ment for the period of observation following the drinking of the coffee. 

 With a planimeter this area measured 4.25 units, and since each unit 

 of area represents a value of 6 calories, the total increment (6 X 4.25) 

 was therefore 26 calories. The basal value corresponding to the period 

 of 3 hours 50 minutes or 230 minutes (230 X 1.15) would be 265 calories. 

 The percentage increase in the metabolism (26 -i- 265) was therefore 

 10 per cent. 1 



The planimeter method used in the coffee and beef-tea experiments 

 for determining the increment in the heat output was also used in the 

 respiration experiments with other food materials for computing the 

 percentage obtained by a comparison of the increment in the heat 

 output with the fuel value of the food material ingested ?'. e., the "cost 

 of digestion." 2 To illustrate this method as employed in experiments 



'See table 68, p. 136. 



J See discussion of these values, p. 335 ct seq. 



