Chap. 3-] Aftian of Vital Air, fcff. 333 



the air was ftill found better, by the nitrous tell, than 

 common air. 



From fome experiments made by Dr. Goodwyn, 

 he concludes that the lungs contain 109 cubic inches 

 of air after a complete expiration ; and that this 

 quantity receives an addition of fourteen cubic inches 

 by infpiration. The dilatation of the lungs, therefore, 

 after expiration, is to their Dilatation after infpiration 

 as 109 to 123. 



One infpiration is commonly performed for every 

 four or five pulfations of the heart, which latter, in 

 different healthy perfons, vary from fixty to ninety in 

 a minute. 



The blood undergoes remarkable changes of co- 

 lour when circulating in the vefifels of an animal 5 in 

 the lungs it acquires a florid hue, which is gradually 

 loft, while the blood is paflmg through the other 

 parts of the body, again to be reftored in the lungs. 

 That the red colour of blood is owing to the influ- 

 ence of vital air is manifeft from actual experiment. 

 Dr. Prieftley introduced different portions of Iheep's 

 blood into different kinds of air, and found always 

 that the blacked parts affumed a bright red colour in 

 common air, and more efpecially in vital air; whereas 

 the brighteft red blood became prefently black in any 

 air unfit for refpiration, as fixed air, inflammable, azotic, 

 and nitrous gas, and after becoming black in the laft 

 of thefe kinds of air, it regained its red colour on being 

 expofed to common or vital air, the fame portions be- 

 coming alternately black and red. 



It is proper, however, to mention, that Dr. Good- 

 wyn introduced four ounces of florid blood, frefh 

 drawn, into a glafs receiver, containing fixed air, and 

 confined it there for a considerable time ; and a]fo re- 

 ceived blood from the carotid arteiy of a fheep into a 

 x phial 



