Volltext: The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea (1)

excretion .of carbon, which immediately on its 
being evolved from the nourishing fluid, en¬ 
tered into combination with the oxygen of the 
air, and wras carried off ; and the chief reason 
for this opinion was, that the volume of oxy¬ 
gen which disappeared in the process, was 
believed to be just equal, in all cases, to that of 
the carbonic acid that appeared. As it is 
known that the volume of any quantity of 
carbonic acid is just the same as that of the 
oxygen contained in that quantity of acid, if 
the fact had been as above stated, the coinci¬ 
dence could hardly have been accidental, and 
the inference would have been nearly inevitable, 
that the oxygen of the atmosphere did not enter 
the nourishing fluids, but merely dissolved and 
carried off the excreted carbon. 
But the numerous experiments of Dr. Ed¬ 
wards* and of M. Du Long,f seem to have 
nearly established the proposition, that in the 
respiration of by far the greater number of 
animals, the volume of oxygen that disappears 
from, is somewhat greater than that of the 
carbonic acid that appears in, the air employed : 
the same result was obtained in experiments 
by Allen and Pepys on birds and if this be 
so, it is certain that the respiration of these 
animals is attended with an actual absorption 
of oxygen, at least to a certain extent. 
This conclusion authorizes us to inquire far¬ 
ther, whether it is not more probable, that the 
whole of the oxygen which disappears from air 
in contact with the nourishing fluid of living 
beings, is absorbed into that fluid, and that the 
carbonic acid which appears is exhaled, ready 
formed, in its place. And several facts shew 
that this is by far the more probable suppo¬ 
sition; and that oxygen is essential to vital 
action, not merely as a means of carrying off 
superfluous carbon, which has become noxious; 
but as itself an ingredient in the nourishing 
fluids, necessary for the maintenance of their 
motion and vivifying power. 
But without entering at length into this 
question, which will be more fully discussed 
under the head of Respiration, it is obvious 
from what has been said, that provision must 
be made, in the œconomy of all living beings, 
for the exposure of their fluids to the air of the 
atmosphere, in circumstances admitting of ex¬ 
halation and absorption ; and it may be farther 
stated, that, in the different classes of animals, 
the amount of this mutual action for which 
provision has to be made, must be proportioned 
to the energy and activity of vital action 
which each animal is destined to exhibit, these 
qualities being very generally found to be 
greater, as the consumption and vitiation of the 
air are more rapid.§ 
These principles explain the intention of 
many different contrivances and arrangements, 
afterwards to be described, which are em¬ 
* De l’Influence des Agens Physiques sur la Vie, 
p. 410, et seq. 
t Journal de Physiologie, t. iv. 
+ See Hodgkin’s Translation of Edwards, p. 486. 
$ See Cuvier, La Règne Animale, t. i. p. 56; 
also Marshall Hall, Philosophical Transactions, 
1832, p. 339. 
ployed in different classes of animals for the 
performance of the function of respiration; and 
the variations of which may be said, in a gene¬ 
ral view, to be determined by two conditions, 
first by the medium in which each animal is 
destined to exist, and secondly, by the inten¬ 
sity and variety of vital actions which it is to 
be capable of performing. 
The importance, to all living beings, of the 
action of oxygen on their fluids is most un¬ 
equivocally shewn by the nature of the fetal 
changes which ensue, when that action is in 
any way obstructed ; i. e. by the nature of the 
changes which take place in death by asphyxia. 
The study of these has long been held to be 
of the highest importance, not only as a car¬ 
dinal point in physiology, but as affording the 
only precise information in regard to the fatal 
tendency of many and various diseases. 
It is chiefly in animals of the highest orders, 
i. e. in warm-blooded animals, that these phe¬ 
nomena have been studied ; and it is to be 
remembered, that in them the subject is ren¬ 
dered more complex by the higher endow¬ 
ments and greater power over all functions of the 
body,which the nervous system there possesses. 
When we trace the connection, in these animals, 
of the different changes that precede the fatal 
event, it is right to bear in mind, that the in¬ 
terruption of the process by which their fluids 
are exposed to the air is equally fatal, not only 
to those animals in which no action of the ner¬ 
vous system is concerned in that process, but 
also in vegetables, where no nervous system 
The phenomena of asphyxia in the higher 
animals are very nearly the same, in whatever 
manner the access of air to the organs of respi¬ 
ration is prevented. This may be done, in the 
case of animals that breathe by lungs, in a 
great variety of ways ; by strangulation or suf¬ 
focation, i. e. by any mechanical means pro¬ 
hibiting the ingress of air by the trachea and 
bronchi ; by submersion in water or any other 
fluid; by confinement in vacuo or in such 
gases as contain no oxygen, but are not them¬ 
selves poisonous, such as azote and hydrogen ; 
by forcible compression of the thorax, prevent¬ 
ing its dilatation ; or by the admission of air 
into free contact with the surface of the lungs 
on both sides of the chest, so as to prevent 
their distension, as in the celebrated experiment 
of Dr. Hooke ; or by the section, either of all 
the separate nerves which move the muscles 
concerned in the dilatation of the thorax in 
inspiration, or of the spinal cord in the upper 
part of the neck, above the origin of the 
phrenics, by which the whole of these nerves 
are simultaneously palsied, as in many ex¬ 
periments of Galen, Cruikshank, Le Gallois, 
and others.* 
In the case of fishes or other animals that 
* These last are the lesions of the nervous sys¬ 
tem which cause sudden death by asphyxia. Sec¬ 
tion of the par vagum, the sentient nerve of the 
lungs, produces death by asphyxia also, but 
slowly, and through the intervention of disease and 
disorganization of the lungs, to be afterwards no¬ 


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