Philosophical Conceptions of Life. 23° 
sary modifications of the primitive rude attempts*, doubts 
are beginning to arise as to whether after all the conditions in 
which the animal is placed in the calorimeter are not so far 
abnormal as seriously to vitiate the results + ; so that, in fact, 
the most approved numerical expressions of the heat-produc- 
tion of the body to be found in the books are based rather 
upon calculation of the amount that ought to be produced by 
the oxidation of an estimated quantity of food than upon 
actual calorimetric observations. 
Nor do we find it any easier when we attempt the actual 
measurement of the amount of work produced by an animal 
from a given amount of food. Indeed, in attempting to for- 
mulate an equation between the potential energy of the food 
and the actual amount of heat and work in any given case, we 
are met with the special difficulty that the animal does not 
evolve less heat because it is doing work than it does when it 
is at rest; on the contrary, it actually evolves more heat, 
consuming for the purpose more food than usual, or, if this is 
not forthcoming, consuming a part of its own reserve of adi- 
pose tissue; so that from this source fresh complications of the 
problem arise. 
The labour and ingenuity with which all these difficulties 
have been encountered is certainly worthy of the highest 
praise, and I willingly admit the probably approximate truth 
of the figures generally in use, say 2} to 2? million gramme- 
degrees as the daily average heat-production of an adult man, 
and 150,000 to 200,000 metre-kilogrammes as his capacity 
for daily mechanical work f. Nevertheless, these figures are 
after all only probable approximations, and there still exists, 
with regard to these questions, a large and inviting field for 
the application of chemical and physical methods to physio- 
logical research. 
All the mechanical work done by living beings is effected 
by means of certain contractions of their soft tissues. The 
movements of the Amoeba, so often described of late years, 
may be taken as the type of the simplest form of these con- 
tractions. Similar movements occur, with more or less 
activity, in the protoplasm of all young cells, and in the 
higher animals are strikingly illustrated by the movements 
ot the white corpuscles of the blood and the wandering cells 
of the connective tissue. In the lowest animal forms-these 
* See H. Senator, ‘‘ Unters. iiber die Warmebildung und den Stoff- 
wechsel,” Archiv fur Anat. Phys. und wiss. Med. 1872, 8. 1. 
+ Foster, p. 368, op. ct. supra. 
} L. Landois, Lehrb. der Phys. des Menschen (Vienna, 1879), 8. 402. 
