RESPIRATION. 253 



7. The quantity of blood that flows to the lungs to be acted 

 upon by the air at one action of the heart is two ounces, and 

 this is acted on in less than one second of time. 8. The 

 quantity of blood in the whole body of the human adult is 

 24 pounds avoirdupois, or 20 pints. 9. In 24 hours 57 

 hogsheads of air flow to the lungs. 10. In the same time, 

 24 hogsheads of blood are presented in the lungs to this quan- 

 tity of air. 11. In the mutual action that takes place be- 

 tween these quantities of air and blood, the air loses 328 

 ounces of oxygen, and the blood 10 ounces of carbon." 



23. The blood, as it goes the round of the system, leav- 

 ing a little bony matter here, a little muscular there ; sup- 

 plying the nails, and the hair, and the skin, and every thing, 

 with the particles which, in the wear and tear of the ma- 

 chine, they have lost ; loses by degrees its bright arterial 

 colour, and by the time it comes round again to the lungs, 

 it is no longer fit to perform its duty ; it has been robbed of 

 all its principles most essential to life, and it must be re- 

 newed and prepared afresh, before it can be of any further 

 use. This is done in the lungs : and this process is what 

 physiologists call the vital part of respiration. 



24. All animals have not lungs, (insects absorb the air 

 from the surface of the body^ so also do many of the family 

 of zoophytes. ^Some have feathery tufts, like a plume of 

 feathers, which they keep in constant motion') while the 

 common earth-worm, or \angle-worm, has a single row of 

 holes along its back, about one hundred and twenty in num- 

 ber, which open each of them into a small respiratory bag, 

 situated between the skin and the intestine/ The leech or 

 blood-sucker, and the lamprey eel, have the same kind of 

 apparatus for breathing. 



25. (Infohes, the gills, which are their lungs, are made up 

 of an infinite number of little fibres, or filaments, set close 

 together, like the teeth of a fine comb, or the barbs of a 

 feather; and these are covered with innumerable small 

 processes, crowded together like the nap of velvet, and over 



22 



