ON ANIMAL HEAT. 567 
Becquerel and Breschet discovered a considerable increase of 
temperature above that of the surrounding parts. 
The great increase of temperature of the uterine system (16) 
during the act of parturition may be explained by the increased 
vascularity of the parts, and by their extraordinary dilatation 
originating an additional source of caloric. That the temperature 
of the parts of the body lessens with their distance from the 
centre of circulation (17) may be accounted for by the decrease 
of elastic arterial tissue as the arteries diminish in size, and by 
the greater comparative surface which the extremities offer for 
radiation. 
Increased or diminished vascularity explains why the temper- 
ature of the brain should be lower than that of the rectum (17). 
That arterial should possess a higher temperature than venous 
blood (18) is further confirmatory of the view I have taken. It 
is also probable that the slight difference of temperature of the 
blood in the two sides of the heart may be occasioned partly by 
the superior muscularity of the left side over the right, and partly 
by its passage through tubes possessing elasticity. 
That animals preserve their caloric at very low temperature (22) 
is not at all incompatible with the view I have taken of its proba- 
ble source. On the contrary, it confirms it ; for by assigning to 
the arterial tunics the chief power of producing heat, we explain 
readily why the body maintains a nearly uniform heat during the 
variations of temperature of the atmosphere. The influence of 
heat and cold on the animal tissues generally, and the arterial 
tissue in particular, is well understood ; the one dilates them, and 
the other renders them more contractile. By putting one arm 
into a bucket of warm and the other into a bucket of cold water, 
we diminish the force of the pulse in the former, but increase it 
in the latter case. The same thing occurs throughout the whole 
body when under the influence of general cold. The arteries be- 
come more fitted to the production of heat by the increased 
tone of their contraction. A circumstance further illustrating 
this view has been observed in animals drowned in hot water, 
when the action of the heart irrecoverably ceases sooner than if 
drowned in cold water. 
It has been already seen (23, 24) that the living animal frame 
may be exposed to high natural or artificial temperatures without 
its own internal heat being materially disturbed. That this is 
mainly attributable to the cooling influences of the skin and 
lungs has been incontrovertibly proved by De la Roche. Under 
ordinary circumstances the production of heat does not exceed 
the degree required for the proper performance of the animal 
functions. There is a balance between the supply and consump- 
tion of it. This takes place when the body is in a quiescent 
