Volume 1

Health lectures for the people.

Date:
1883-1892
Catalogue details

Licence: Public Domain Mark

Credit: Health lectures for the people. Source: Wellcome Collection.

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    burns itself nor allows anything else to burn in it. The main function it fulfils in the atmosphere is to dilute the oxygen and give bulk and weight to the air. The breathing of man and other animals, otherwise known as respiration, is practically a process of combustion. The air which is inhaled enters the lungs and then passes through into the blood. The lungs contain from 5 to 6 ^millions of air cells, which though minute in size, yet from their numbers have a large surface of from 10 to 20 square feet, and such air cells inpinging upon the blood vessels enable the air which is breathed in by the lungs to enter the blood. The aerated blood is constantly circulating through the animal system, and the oxygen of the air in the blood burns up animal matters, so that when the blood returns to the lungs it has lost much of its oxygen, and contains instead of it a decided proportion of another gas formed of carbon and oxygen, and known as carbonic acid. This gas can be produced out of the animal system by burning a piece of carbon in a vessel containing air or oxygen, and may be proved to be carbonic acid by adding some clear lime water to the vessel and agitating, when a milky liquid will be obtained owing to the formation cof carbonate of lime or chalk. In a similar way, if a man breathes into clear lime water, the carbonic acid which has been produced by the combustion in the animal system at once renders the lime water of a milky nature. The same result will be obtained by breathing into an empty jar, and thereafter adding the lime water and agitating. We can thus prove the identity of the combustion of carbon out of the body, with the respiratory processes proceeding within the animal system, and demonstrate that carbonic acid is the product of both processes. The change which takes place in the air during the act of re- spiration is very decided. When taken in a dry state, the atmosphere in country places or rural districts contains from 20*96 to 20*98 per cent, of oxygen, and only 0*04 per cent, of carbonic acid, and in town districts from 20*87 to 20*90 per cent of oxygen, and 0*04 per cent, of carbonic acid. The pro- portion of the latter is therefore very small, and indeed is only 4 parts in 10,000, or 1 part in 2500 parts. But when the