1798.] 
independent of the portion of vital air 
which had been converted into carbonic 
acid gas, a portion of that which entered 
into the lungs was not returned in the 
aeriform ftate: the refult of which was, 
that during refpiration one of two things 
came to pafs; either, that a portion of 
vital air united with the blood, or, com- 
bined with a portion of hydrogene, and 
formed water. Unfortunately, the ex- 
periments which we are going to relate, 
notwithftanding their utility, are not fuf- 
ficiently decifive on that point. 
It had been already announced, that 
blood, during its circulation, undergoes 
a remarkable change of colour; that 
when it paffes into the capillary veins, it 
takes a deep livid colour, which foon 
grows brighter, and becomes a vermilion 
red whilft it paffes the lungs; but the 
caufe of this phenomenon. was unknown 
until Cigna and Pricftley obferved, that 
expofing venal blood to vital air, gives it 
the colour of arterial blood, which, when 
expofed to hydrogene gas, reaffumes the 
appearance of venal blood. TI have re- 
peated thefe experiments and have found 
that arterial blood put in contact with 
hydrogene gas, abforbs that fluid, and 
takes the livid dark colour of venal blood, 
whilft this latter, when in contact with 
vital air, converts it in part into carbo- 
nic acid gas, and then.acquires the bright 
vermilion-colour of arterial blood. 
The refult of Hamilton’s experiment 
is the fame; he made three ligatures on 
the jugular vein of a cat, and having let 
ut the blood contained between two of 
the ligatures, he’ introduced hydrogene 
gas, and retained it by clofing up the 
aperture through which it was inferted ; 
he then untied the middle ligature, and 
the blood contained between that and the 
third became in contact with the nydro- 
gene gas; and, in ‘an hour’s time,. this 
blood had acquired a colour nearly as 
dark as ink. 
At the fame time, he made two liga- 
tures on the crural vein of the fame ani- 
mal, and there intercepted, for near an 
hour, the fame quantity of blood as in 
the firft experiment ; which, when taken 
away, was not near fo dark as the former. 
The venal blood then undergoing in 
the lungs the fame change of colour as 
when expofed to oxygene gas, we may 
conclude with Lavoifier and Crawford, 
that the venal blood, in pafling into the 
lungs, takes a vermilion colour, becaufe 
it yields a portion of its hydrogene gas 
to the vital air; andthat, afterwards, in 
the courfe of its circulation, it grows 
Seguin on Refpiration and Animal Heat. 
95 
darker becaufe it combines with the hy- 
drogene which the fyitem affords it: and, 
as all the hydrogene gas dvawn from ani- 
mal fubfances keeps a portion of carbom 
in folution, the refult during infpiration 
is, that a portion of the vital air received 
into the lungs combines with the carbo- 
nated hydrogene difengaged from the 
blood, and forms carbonic acid gas with 
the carbon, and water with the hydre- 
gene. | 
It cannot here be objected, that hydro- 
gene gas and vital air do only combine 
when a heated body is preiented to them; 
the experiments both of Bertholet and 
of Prieftley prove effectually, that hydro- 
gene, when near being fluid, unites with 
vital air, in the common temperature of 
the atmofphere. } 
It was alfo Lavoifier who firft attributed 
animal heat to this decompolition of vital 
air in the lungs: he exprefled this opi- 
nion in a memoir read before the fociety 
in’ 1777,.if not, as an.abfolute truth, at 
leaft_ as a conjecture very much refem- 
bling it. e 
Crawford had, the fame year, a fimilar 
opinion, and in 1779 publithed a very 
interefting work, in which he collected a 
ferics of experiments adapted to realize 
this hypothefis. One otf thefe experi- 
ments ferved to explain the permanence 
of the temperature in different parts of 
our fyftem. 
According to. Crawford, the calorific 
capacity of arterial blood -is .to that of 
venal blood, as 11.5 to nearly 10; that 
isto fay, if a quantity of caloric railes 
the temperature of a pound of arterial 
blood to ro degrees, that fame quantity 
of caloric will elevate the temperature of 
a pound of venal blood to 11.5 degrees. 
The attraction of carbonated hydre- 
gene for oxygene being then ftronger 
than the united attraction of oxygene for 
caloric, and the carbonated hydrogene 
for blood; the vital air is dec*inpoled 
during infpiration; and in that cafe it 
abandons a portion ef its {pecific caloric 
which unites with the blood, the capacity 
of which is increafed by the lofs of a por- 
tion of its caroonated hydrogene: but 
thé arterial blood, in its circulation af- 
terwards, receives from the fyftem a 
certain quantity of carbonated hydro- 
gene; and during: this abforption, its 
capacity being diminifhed, it abandonsa 
portion.of the caloric which it had ab- 
forbed in the lungs ;.. this ¢aloric then 
{fpreads itfelf over the furrounding hu- 
mours, and promotes their temperature 
in a manner neatly uniform: thus, it is 
te 
