--I mixed, in the same proportions, fire-air and
air vitiated by peas, and filled a bladder with it. Then when I had
completely exhaled the air present in my lungs, I respired this newly
compounded air as many times as possible. I then found that it contained
very little aerial acid in it, and when this was separated from it, it
extinguished fire. I believe that one must ascribe to the blood present
in the pulmonary veins, the effect which animals endowed with lungs have
upon the air. The following experiment gives me cause for this.

It is known that freshly drawn blood, when it stands in the open air,
assumes a fine red on the surface, and that the under portions likewise
become red when they come into contact with the air. Does the air in
this case undergo any alteration? I filled a flask one third part with
freshly drawn ox blood, closed it tightly with a bladder, and shook up
the blood frequently. Eight hours afterwards I neither found aerial acid
in this air, nor that its bulk was diminished; but the flame of a candle
was immediately extinguished in it. I made this experiment in winter
time, from which may be gathered that the effect cannot be ascribed to
any putrefaction, for this blood was found still fresh 6 days
afterwards, and besides, all putrefactions produce aerial acid. I was
now curious to know how fire-air by itself would behave with animals and
plants.

+90. Seventh Experiment.+--(_a._) I put 2 ounces of nitre into a small
glass retort upon glowing coals, and attached a large bladder softened
with water (Sec. 35), and allowed the nitre to boil until I had received
3/4 of a quart of fire-air in the bladder. I then tied up the bladder
and separated it from the retort; I then placed a tube in its opening,
and after I had completely emptied my lungs, I began to respire air from
this bladder (Sec. 84). This proceeded very well, and I was able to make 40
inspirations before it became difficult for me; eventually I expelled
the air again from my lungs as completely as possible. It did not seem
to have diminished particularly, and when I filled a bottle with it and
introduced a burning candle, this still burned. I then began to respire
this air anew, and was able to make 16 more inspirations. It now
extinguished the flame, but I found only some traces of aerial acid in
it. (_b._) I was surprised that I was not able the first time to take
away from this air the property of allowing fire to burn in it; I
thou