LATER INVESTIGATIONS 13 
LATER INVESTIGATIONS ON METABOLISM IN ITS RELATION 
TO MUSCULAR WORK AND ANIMAL HEAT. 
Beginning with 1850, investigations on the relation between metabolism 
and muscular work formed a considerable part of the researches of many 
physiologists. As time passed, the technique was more carefully developed 
and accuracy increased, since each succeeding investigation improved or 
attempted to improve upon the earlier ones; rapid progress in this field of 
research was thus assured. The literature, however, has its greatest value as 
a record of progress rather than as a series of mathematically exact contribu- 
tions to the development of the general problem; consequently it is unneces- 
sary to enter into an exhaustive digest of each paper, especially as this has 
already been admirably done in a number of articles which have appeared in 
handbooks and encyclopaedias. A brief statement of the researches and the 
methods employed will therefore suffice, but in the subsequent discussion 
of the results of this investigation, specific reference will frequently be made 
to such portions of the earlier papers as deal particularly with the points 
under consideration. 
The simultaneous measurement of the products of respiration and the 
heat outgo in experiments on man was first attempted in 1857 by Hirn. a The 
study of the mechanical equivalent of heat which was engaged in at this time 
by many scientists led this investigator to make an attempt to deduce the me- 
chanical equivalent of heat from a comparison of the heat and work simulta- 
neously produced by a man with the calorific equivalent of the amount of oxygen 
consumed. Although his experiments were wholly unsuccessful, 6 they marked 
a step in the attempt to establish the law of the conservation of energy. 
The first extensive investigation into the influence of muscular activity 
upon the carbon-dioxide production was that made by Edward Smith, 
who early recognized the difficulties of computing the carbon-dioxide output 
of any individual owing to the unknown factor of muscular exertion. Smith, 
employing a mask and an absorbent for carbon dioxide, together with a 
gas-meter, estimated the amount of carbon dioxide excreted per hour under 
various conditions of muscular activity with and without food. 
While walking at the rate of 2 miles per hour during three-quarters of an 
hour, and carrying a spirometer weighing 7 pounds, the investigator expired 
18.1 grains of carbon dioxide per minute and 25.83 grains per minute while 
walking at the rate of 3 miles per hour. These quantities represent 1.85 and 
2.64 times that of rest in the sitting posture. From these experiments Smith 
computed the quantities of carbon dioxide expired in quietude, by the non- 
laboring class, and by laboring individuals. In quietude the results were 
26.193 ounces of carbon dioxide per day, this being equal to 7.144 ounces of 
carbon; with the non-laboring class, 31.824 ounces of carbon dioxide, equal to 
8.68 ounces of carbon; and with the laboring class, 43 ounces of carbon 
dioxide, equal to 11.7 ounces of carbon, with a general average of 33.67 ounces 
of carbon dioxide and 9.18 ounces of carbon per day. 
a Him, Recherches sur l'equivalent mecanique de la chaleur, Paris, 1858. This paper, subsequently redis- 
cussed by Him (La thermodynamique et le travail chez les etres vivants, Paris, 1887), was severely 
criticized by Chauveau (Arch. d. Physiol, norm, et pathol., 1897, 9, p. 229). 
6 See Weiss, Physiologie generate du travail musculaire et de chaleur animate, Paris, 1909, p. 140, for a criti- 
cism of Hirn's results. 
c Smith, Philosophical Transactions, 1859, 149, p. 681. 
