Elements of human physiology / by Henry Power.

  • Power, H. (Henry), 1829-1911.
Date:
1888
Catalogue details

Licence: Public Domain Mark

Credit: Elements of human physiology / by Henry Power. Source: Wellcome Collection.

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    Oxygen.—This gas is one of the most widely dis- tributed substances in nature, and is essential to the existence of both plants and animals. It exists in the free state in the air, but, so far as is known, it is not liberated in that state by any agent, except by the green colouring matter of plants under the influence of sunlight. It forms a large proportion of the gases contained in water. A peculiar allotropic modifica- tion of it, named ozone, OgO, is present in fresh air, but seems to be absent where much organic impurity exists. It is the only elementary body which directly participates in the vital processes of plants and animals, and it is essential to their maintenance. By its union with carbon and hydrogen it liberates the heat by which the temperature of the higher animals is maintained. About 7,000 grains are daily re- quired. JVitrog-en.—It is noticeable that nitrogen, an element that has so few and such relatively feeble affinities, should enter into the composition of every living organism ; yet it is perhaps to its presence that the extraordinary variety that characterises the func- tions, the unceasing change that is manifested in the tissues of plants and animals, is essentially due. Having no strong attraction, like that of oxygen for carbon, or of hydrogen for oxygen, it readily permits the decomposition and disintegration of the substances into whose composition it enters; and the elements with which it is combined (chiefly carbon and hydro- gen) readily shift their position, and form sometimes more, sometimes less^ complex molecules. Nitrogen enters into the composition of the most explosive compounds with which the chemist is acquainted, and many of the phenomena presented by nerve and muscle call to mind and have actually been likened to an explosion. Animals derive their nitrogen ex- clusively from, plants. Plants obtain their supplies