from Br. Thornton. 225 



and therefore must arise from the indigo and purple of the 

 third order, and not from the indigo and violet of the se- 

 cond ; and consequent!)' by that table the tingeing corpus- 

 cles of the blood are lessened in the lungs. 



" Hence it appears that the acid parts of tl'.e air dissolve 

 or attenuate the blood in the lungs. 



"■ Oil of vitriol and water poured successively into the same 

 vessel grow verv hot in the mixing: aquafortis, or spirit 

 of vitriol, poured upon filings of iron, dissolves the fihngs 

 ,with a great heat and ebullition: and the acid of the air 

 constantly applied to sulphureous and unctuous substances, 

 when once they are kindled, continues to dissolve them with 

 the heat of fire and flame. 



**■ f'rom these experiments we learn, that it is the nature 

 of acids to dissolve bodies with heat ; and therefore, since I 

 have shown that the acid of the air dissolves the blood, it 

 must be allowed that it warms the blood at the same time 

 it dissolves it. 



" When animals are deprived of the acid of the air, the 

 pulse in less than one minute of time becomes small and 

 quick ; as may be observed in a dog, when his lungs are 

 made flaccid and without motion by laying open his tliorax. 

 Upon emptying my lungs of air as much as I could j and 

 then stopping my breath, my pulse has grown small and 

 quick> with a kind of trembling convulsive motion, in less 

 than half a niinule of time. And Thurston observed the 

 pulse to grow smaller on an intermission of respiration, and 

 greater again on repeating it. 



"tience it appears that the motion of the heart lessens im- 

 mediately on animals being deprived of the acid of the air; 

 and consequently that this acid, by dissolving or attenuating 

 the blood and preserving its heat, keeps up the iDotioji of 

 the heart. 



" Therefore the proposition is true. 



'^ Scholium. 



" 1. The motion of the lungs in breathing is no otherwise 

 necessary to the life of animals, than as by this motion the 

 lungs receive a constant supply of fresh air. 



" For Hook, after he had laid open the thorax of a dog, 

 cut away his ribs and diaphragm, and taken off the peri- 

 cardium, kept him alive, before the Royal Society of Lon- 

 don, above an hour, by blowing fresh air into his lungs 

 with a pnir of bellows. It was observed, that as often as he 

 left off blowing, and suffered the lungs to subside and lie 

 jtill, the dog presently fell into dying convulsive motions, 

 and soon recovered again on renewing the blast. After he 

 had done this several times with like success, he pricked all 



VoL.XVHl.No. 71. P tb.' 



