Physiological Researches on Life and Death

by Xavier Bichat

2dly. The celebrated experiment of Hook, in which the enfeebled movements of the hearts of animals in a state of asphyxia are accelerated by injecting air into the lungs, is very well explained. The red blood penetrates into the fibres of the heart, and puts an end to the debility induced, by the influx thither of the black blood.

3dly. I do not believe, that motion can ever be restored to the heart, when once it has been wholly annihilated by the presence of venous blood. In this I have never succeeded, though I have often attempted it. Many authors, however, pretend to have done so. If the heart be reanimated by arterial blood, it is necessary at any rate, that such blood, should pass into it, now in what way can it arrive there, if the circulation have entirely ceased.

We must observe, however, that there are two cases of interruption in the action of the heart from asphyxia. Sometimes there supervenes a syncope which arrests the movement of this organ, before the black blood has been able to produce such effect; and here it is manifestly capable of excitement, from the presence of the red blood, just as it is from the application of any irritating cause; but when it has been injected with venous blood, it then contains within itself the principle of its inertia, which can be removed only by the contact of arterial blood with it; but such contact is become impossible.

I was very desirous of knowing what the influence might be of the different gases when inspired upon the colour of the blood. Accordingly I successively adapted to the pipe different bladders, containing hydrogen and carbonic acid gas.

The animal alternately swells and contracts the bladder by the different motions of the thorax. It is calm at first, but at the end of three minutes, begins to be agitated; its respiration is now hurried and embarrassed, and at the end of four or five minutes, the blood of the carotid is black.

Whichever of the two gases be employed, there is little difference in the above phenomena. This remark should be compared with those of the Members of the Institute, who have assured us that complete asphyxia supervenes only after an interval of ten minutes, with pure hydrogen, and at the end of two minutes with carbonic acid gas. The black blood must continue, therefore, to circulate for a longer time in one than in the other kind of asphyxia here spoken of. This circumstance confirms some reflections which I shall have occasion to offer upon the difference of asphyxiæ.

For what reason should the blood be a longer time in losing its colour, when bladders of non-respirable air are fixed to the pipe, than when the cock is simply turned? The reason of this is evident. By the different motions of the lungs, the air is expelled and reabsorbed, the respirable portion of it must consequently be successively presented to the capillary orifices, by which it is transmitted to the blood.

On the contrary, when the pipe is simply shut, the air it is plain has not the same influx and efflux; in comparison with such motion, it may be said to stagnate so that the respirable portion of that which is enclosed in the bronchial cells is exhausted, and the blood ceases to be coloured, though there remain in the trachea and its larger divisions, a considerable quantity of fluid, which has not been despoiled of its vivifying principle. Of this we may be certain, after the death of the animal, by cutting the trachea under the pipe, and plunging a bougie into it. The process by which the blood gains its red colour appears to take place only at the extremities of the bronchiæ, the inner surface of the larger aerial vessels, has nothing to do with this phenomenon.

We may convince ourselves of the reality of the explanation which I have offered, if we pump out the air of the lungs, before we fit the bladder to the trachea; for in such case, the animal must breathe the air of the bladder without mixture. Here the change of the blood to black is almost sudden, but here also, as in the preceding experiment, there is little difference in the phenomena, whatever gas we employ. I have chosen the two gases above mentioned, because they enter into the phenomena of natural respiration.