Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Todd, Robert Bentley
the greatest possible number of phenomena 
connected with animal heat ; and in determin¬ 
ing the physiological conditions of its produc¬ 
tion, we shall lay up a store of theoretical 
knowledge peculiarly applicable to practice, 
the end and object of all physiological inves¬ 
The means of comparing these modifications, 
however, and of judging of their importance 
are not always easy. We shall do as much as 
the actual state of our knowledge permits if 
we inquire first, by what means we can ap¬ 
preciate the modifications relative to the arterial 
1. As regards the quantity of the arterial 
blood, we shall view this point of the inquiry 
less with reference to the whole amount of 
blood circulating in the body, than to the 
quantity which is formed at a time, as it were, 
in the lungs; because it is evident that if the 
arterial blood influences the phenomenon of 
heat, the more that is formed at any given 
time the greater ought to be the direct or in¬ 
direct influence upon the production of heat. 
a. As it is not always possible to have a direct 
and precise measure of the relative quantity of 
blood in the organs, we must be content with 
an approximative mode of estimating this, 
which consists in ascertaining in what degree 
the lungs are loaded with blood. b. An aid to the 
judgment may also be derived from the relative 
size of the lungs, the tissue being presumed to 
be nearly alike throughout their entire mass, 
c. With an equal volume of lungs, the greater 
or less compactness of the tissue must be taken 
into the account. The closer the tissue is, 
the more are the surfaces in contact with the 
air multiplied, d. The extent and rapidity of 
the respiratory motions form another element 
in the calculation ; for to increase the amount 
of relation with the air is analogous to the for¬ 
mation of a larger quantity of arterial blood 
within a given time. 
All the foregoing data refer to the absolute 
or relative quantity of arterial blood. But 
there are other particulars connected with its 
constitution which it is necessary to mention. 
The blood, for instance, is composed of a fluid 
and solid part, the latter existing under the 
form of globules. It is obvious that the fluid 
is not the characteristic part of the blood, in¬ 
asmuch as this is met with elsewhere, whilst 
the globules of the blood are only known as 
constituents of this fluid. The arterial blood 
consequently ought to have qualities by so much 
the more distinctive and energetic as it con¬ 
tains a larger proportion of globules. Now 
this is a character that may be appreciated with 
exactness, and measures of it have been given. 
But the globules of the blood are not in¬ 
variably of the same nature, a fact which may 
be judged of by outward and very obvious and 
appreciable characters, namely, size and form. 
The smallness and more or less perfectly sphe¬ 
rical or rounded form of the blood-globules 
distinguishing animals with warm blood, co¬ 
incide in the Vertebrata with a higher capacity 
to produce heat. For we do not institute this 
comparison here save in reference to animals 
included in this division, inasmuch as the cha¬ 
racters of the blood have only been studied 
under these relations among them. We shall, 
therefore, hold the energy of the calorific power 
to be connected with the smallness and rounded 
form of the globules of the blood in vertebrate 
2. The materials of the blood being sup¬ 
plied by the digestive apparatus, we might 
judge, all things else being equal, of the per¬ 
fection of the blood by the perfection of this 
apparatus. But there is likewise a necessary 
co-relation between the result of the function, 
and the aliment; for instance, when the ap¬ 
paratus shall be found nearly alike in any two 
cases, the difference of food necessarily in¬ 
fluencing the qualities of the blood, the com¬ 
parison must be established, every other cir¬ 
cumstance being equal, according to the higher 
or lower nutritive qualities of the food. 
As the use of the arterial blood is to excite 
and nourish the different parts of the body, 
there will be a necessary correspondence be¬ 
tween the blood and the result of the nutrition 
which may become manifest in the nature and 
quality of the tissues. And in this case it 
would be fair to make use of these characters 
of tissues to form an estimate of the nature of 
the blood in reference to its aptitude to pro¬ 
duce heat ; and this we shall accordingly do. 
But even in the event of all these characters 
failing us, there is another source whence we 
can derive comparative measurements, which 
are susceptible of very rigorous application. 
Since it is necessary that the venous blood 
should pass through the lungs in order to be¬ 
come arterial from contact with the air of the 
atmosphere, it is obvious that it cannot un¬ 
dergo any change in its constitution without 
the air at the same time suffering a change. 
That the air is altered by the respiratory act is 
well known to all, and as there is a necessary 
co-relation between the blood aerated during 
respiration and the air which it alters, the 
amount of alteration undergone by the one 
may be estimated from the change suffered by 
the other. The quantity of air altered by re¬ 
spiration, all other things being equal, ought 
to be found in relation with the production of 
The different characters which we have men¬ 
tioned all refer directly or indirectly to the 
blood. There still remains one of another 
order which may also serve us as a guide in 
making comparisons in reference to the pro¬ 
duction of heat. The allusion here made is 
to the nervous system, the superior value of 
which in warm-blooded animals has already 
been commented on. It is thus, then, that we 
may assume the predominance of the nervous 
axis, and particularly of its encephalic ex¬ 
tremity, as a condition favourable to the pro¬ 
duction of heat, and which, in circumstances 
of parity among the other conditions, must 
tend to the production of a greater quantity of 
heat. Such are the modes of proceeding which 
we shall follow in investigating the modi¬ 
fications of the organic conditions and of the 
functions which coincide with the greater evo-


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