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POPULAR SCIENCE REVIEW. 
stituents of the blood traversing its capillaries. Immediately, 
however, the nervous impulse for action arrives at each fibre, 
chemical change is started ; as when the metals of the battery- 
cell come in contact with the acid, heat is developed, and work 
is performed. This heat adds to the warmth of the body, as 
may be seen by the rise in temperature attending a walk in the 
accompanying instance. In this case the thermometer for 
some time before the commencement of the walk — which was 
at the rate of four miles an hour on level ground — had registered 
98°, my time being employed in standing about : — 
Time. 
Temperature, j 
12-45 
1- P.M. 
1-15 
1-30 
1- 45 
2- P.M. 
2-15 
2-30 
98- 4 
99- 1 
99-5 
996 
99-675 . 
99-65 
99-2 
98-95 
Walking for 5'. 
Walking. 
f) 
V 
Ceased walking 5'. 
Standing. 
V 
But during rest the voluntary muscles do not act ; it is not 
therefore to them that the ordinary heat of the body can be 
ascribed. There are, however, muscles which are continually 
acting, such as the heart and respiratory muscles. These do a 
large amount of work, the former driving the blood through 
the whole circulatory system at an enormous rapidity, under 
great pressure ; the latter expanding the chest nearly twenty 
times a minute. The work they perform being so great, the 
necessary chemical decomposition appears mostly as such, in- 
stead of as heat in the organs themselves. Nevertheless, it not 
manifesting itself externally, shows that it must all be ulti- 
mately converted into heat in the system, in the resisting ca- 
pillaries, and in the chest-wall. 
Here, therefore, is a considerable source of heat, to which must 
be added the vermicular movement of the intestines, together 
with that of the sphincters. Statistics for the calculation of 
whether these forces are sufficient to account for the total heat 
of the body are not forthcoming. The amount of blood which 
traverses the large arteries in a given time is not yet known, 
and the value of the minor forces is far from easy to estimate. 
There is no doubt, however, that the heat developed by these 
processes is considerable, and that rise in temperature is cor- 
related with activity of function. I have elsewhere* given rea- 
sons to show that the pressure of the blood in the arteries is 
* Journal of Anat. and Phys., vol. viii. pp. 54, 189. 
