174 
AMT. 
Fie. 2. Curves of a normal biological process 
£ proceeding at a constant rate, and the same 
process under abnormal conditions with a variable 
rate, F. 
RATE 
Fig. 3. Curve of a tale process which is 
studied by measurements of its rate made at fre- 
quent intervals. The shaded portions represent 
periods during which measurements are made. 
The unshaded portions represent intervals during 
which there are no measurements. 
mine the rate at various periods as shown in 
Fig. 3, in which the periods during which the 
rate is measured are shaded while the intervals 
during which no measurements are made are 
unshaded. 
We can determine the time necessary to 
SCIENCE 
[N. 8. Von, XLVIII. No. 1233 
perform 4 given amount of work and take its 
reciprocal as the rate: this rate is of course 
an average for the whole period. If the rate 
is changing during the period the average 
rate probably occurs near the middle of the 
period; hence we may place the ordinate 
representing the rate in the middle of the 
period as shown in the figure. The resulting 
curve can be transformed into a curve of the 
type shown in Fig. 2 by finding the total 
amount of work performed at any given time: 
this is accomplished by finding the area en- 
closed by the curve and the ordinate of the 
time chosen (since this area is the product 
of rate by time, it gives the amount of work 
performed). 
Summary.—Measurements of the relative 
rates of biological processes are frequently 
made in a faulty manner which may easily be 
avoided by a slight change of method. 
Usually it is preferable to compare the times 
required to perform a given amount of work 
(or to bring the reaction to the same stage) 
rather than to compare the amounts of work 
performed in a given time. 
W. J. V. OsterHouT 
LABORATORY OF PLANT PHYSIOLOGY, 
HARVARD UNIVERSITY 
HOW FOOD AND EXERCISE INCREASE 
OXIDATION IN THE BODY 
Lavoisier, shortly after his discovery that 
oxygen supported combustion, showed that 
physical work increased oxidation in the body, 
thus giving rise to the energy for the work. 
He also found that the ingestion of food in- 
creased oxidation. Rubner? showed that of 
the food-stuffs, meat increased oxidation most, 
fat next, and sugar least. The present in- 
vestigation was begun in an attempt to find 
out how physical work and the ingestion of 
food increase oxidation in the body. We 
had already found that whatever increased 
oxidation in the body also stimulated the liver 
to an increased output of catalase, an enzyme 
1 Lavoisier, Mem. de 1’Acad. des Sc., 1780. 
2 Rubner, ‘‘Hnergiegesetze,’’ 322. 
8 Burge, Neill and Ashman, American Journal of 
Physiology, Vol. XLV., No. 4, pp. 388-395, 500- 
506. ‘ 
