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 (§ 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 (§ 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 thought that perhaps the great humidity prevented me from drawing this air into my lungs so often as was really possible. Accordingly I repeated the same experiment, only with this difference, that I put a handful of potashes into the bladder before the fire-air was driven into it. I then began to draw this air into my lungs, and counted 65 inspirations before I was compelled to desist. But when I lowered a burning candle into this air, it still burned well, although only for a few seconds.