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POPULAR SCIENCE REVIEW. 
number of deatbs_, and it is to be admitted that to a certain 
extent tbe reason is clear. Without entering on the question 
which the old Greeks so warmly contended for — Heraclitus 
above them all — that heat is the animating principle of all 
living organisms^ we may accept that in the evolution of force 
from the body, as represented by its power of producing force 
in the form of heat, we have a measurement of the capacity of 
the body to sustain force, which is only another phrase for 
expressing the resistance of the body to death. For example, 
if we assume that a healthy man of twenty-nine years, respires 
four hundred and fifty cubic feet of air per day, and by com- 
bustion of his carbon, evmlves as much heat as would raise 
fifty pounds of water at 32° Fahr. to 212° Fahr. under all 
ordinary temperatures, which is about the fact, and if we 
assume that another man at thirty-nine shall not be able at 
any temperature to respire so much air, and shall not be able 
to evolve as much caloric as would raise forty-four pounds 
o£ water from 32° to 212° we see a general reason why the 
latter man should feel an effect from a sudden change in the 
temperature of the air which the younger man would not feel; 
and if we assume, further, that a man at eighty-four, in the same 
time would evolve as much force as would raise only eleven 
pounds of water from 32° to 212°, we see a general reason that 
he should suffer much more from a decrease of external tem- 
perature than either of the two younger men. 
It behoves us, however, to know more than this general 
statement of an approximate fact : we ought to understand 
the exact method by which the reduction of temperature 
influences, and the details of the physiological processes 
that are connected with the phenomena. I will try and 
explain these clearly, although I know they are not easy of 
explanation. When a human body is living at the age 
where the period of growth has ceased and the period of 
decay has not commenced, and when it is quite healthy, it 
generates, by its own chemical processes, so much heat or force 
as shall enable it, within given bounds, to move its own 
machinery, to call forth at will a limited measure of extra force 
which has been lying latent in the organism, and to supply a 
fluctuating loss that must be conveyed away by contact with 
the surrounding air, by the earth, and by other bodies that it 
may touch, and which are colder than itself. There is thus 
evolved in the body, applied force, reserve force, and luaste 
force, and these distributions of the whole force generated, 
when correctly applied, maintain the perfect organism in such 
balance that life is true and steady. So much active force 
carries with it the power to perform so much labour ; so much 
reserve force carries with it the power to perform a measure of 
