Conversations on Chemistry, V. 1-2 / In Which the Elements of that Science Are Familiarly Explained and Illustrated by Experiments

by Mrs. Marcet

MRS. B.

By RESPIRATION. This is one of the grand mysteries which modern chemistry has disclosed. When the venous blood enters the right ventricle of the heart, it contracts by its muscular power, and throws the blood through a large vessel into the lungs, which are contiguous, and through which it circulates by millions of small ramifications. Here it comes in contact with the air which we breathe. The action of the air on the blood in the lungs is, indeed, concealed, from our immediate observation; but we are able to form a tolerably accurate judgment of it from the changes which it effects not only in the blood, but also on the air expired.

The air, after passing through the lungs, is found to contain all the nitrogen inspired, but to have lost part of its oxygen, and to have acquired a portion of watery vapour and of carbonic acid gas. Hence it is inferred, that when the air comes in contact with the venous blood in the lungs, the oxygen attracts from it the superabundant quantity of carbon with which it has impregnated itself during the circulation, and converts it into carbonic acid. This gaseous acid, together with the redundant moisture from the lungs[*], being then expired, the blood is restored to its former purity, that is, to the state of arterial blood, and is thus again enabled to perform its various functions.

CAROLINE.

This is truly wonderful! Of all that we have yet learned, I do not recollect any thing that has appeared to me so curious and interesting. I almost believe that I should like to study anatomy now, though I have hitherto had so disgusting an idea of it. Pray, to whom are we indebted for these beautiful discoveries?

MRS. B.

Priestley and Crawford, in this country, and Lavoisier, in France, are the principal inventors of the theory of respiration. Of late years the subject has been farther illustrated and simplified by the accurate experiments of Messrs. Allen and Pepys. But the still more important and more admirable discovery of the circulation of the blood was made long before by our immortal countryman Harvey.

EMILY.

Indeed I never heard any thing that delighted me so much as this theory of respiration. But I hope, Mrs. B., that you will enter a little more into particulars before you dismiss so interesting a subject. We left the blood in the lungs to undergo the salutary change: but how does it thence spread to all the parts of the body?

MRS. B.