Physiological Researches on Life and Death

by Xavier Bichat

6thly. The alteration of colour in the serous membranes is much more quickly effected than it is in the mucous membranes. Of this we may assure ourselves by comparatively examining the outer and inner surfaces of the intestines, while the pipe in the trachea is shut; in the serous membranes, the livid tint which they assume, depends upon the vessels, which creep underneath them, and not on the blood by which they are penetrated. Now as these vessels are considerable, the black blood must flow into them almost as soon as it is produced. In the mucous membranes on the contrary, and in all cicatrices, the colour which they take on in asphyxia, is made by the capillary system of the membrane itself, which system is much more tardy than the other, to receive the black blood, and to be penetrated by it; so much so indeed, as to refuse it in some parts. I have many times seen the membrane of the nasal fossæ very red in asphyxiated animals, while that of the mouth has been quite livid, for there are parts into which as I have said the black blood will not penetrate at all, and then they preserve their natural colour. 2dly. There are others into which it evidently passes, but where it stops, and then a simple change of colour is observed, if it have penetrated but in small quantity; and again, if it have penetrated in a considerable quantity, together with such change of colour, there will be observed a tumefaction of the part. 3dly. In other cases, the black blood merely traverses the parts, without stopping in the capillary system, and passes at once into the veins, as the red blood does.

In the first and second case, the general circulation experiences an obstacle which puts a stop to it in the general capillary system. In the third, which is much more universal, it is in the capillaries of the lungs that the blood is at last arrested, after having circulated in the veins.

These two sorts of impediment coincide with each other, in many instances. Thus in asphyxia, a part of the black blood which circulates in the arteries stops in the face, upon the mucous surfaces, in the tongue, and in the lips, while the other, and much the larger quantity, finds no impediment in the general capillary system, and is finally arrested in the lungs.

What is the reason, why certain parts of the capillary system refuse to admit the venous blood, or if they admit it, do not pass it on to the veins; while others are less enfeebled by it, and transmit it as freely as ever. All this must certainly depend on the relation existing between the sensibility of each part and the venous blood.

I was desirous of making use of the power, which we possess, of changing the colour of the blood, for getting some insight into the influence of the circulation of the mother, upon that of the fœtus; accordingly I procured a bitch big with young, and asphyxiated her, by closing a tube, adapted to the trachea. About four minutes after she had ceased to breathe, I opened her; the circulation was going on. I then cut into the matrix, and exposed the cord of two or three of the fœtuses. The artery and the vein, were both of them full alike of venous blood.

Had I been able to procure other bitches in a similar state, I should have repeated this experiment in another manner. I should in the first place have compared the natural colour of the vein, with that of the artery. In many of the young of the guinea pig, the difference appeared to me to be much less than it is in the adult animal. In many circumstances indeed I could perceive no difference whatever. Both the arterial and venous blood were equally black, though the respiration of the mother was in no wise impeded by the opening of the belly. Secondly, I should have closed the tube in the trachea, and then have observed whether the change in colour of the umbilical artery of the fœtus (supposing the blood of the artery to be different from that of the vein) were correspondent with that, which would inevitably take place in the blood of the mother. Experiments made with a view to these circumstances, and on large animals, might probably throw much light upon the mode of communication, between the mother and the fœtus. Observations are also much to be desired, with respect to the colour of the blood in the human fœtus, and the cause of its passage from a livid colour, to the very marked red which it assumes, some little time after birth.[95]

I might add a number of examples to these, which I have already related of the blackening of the organs by the venous blood. Thus, the kidney of a dog exposed, while the animal is dying of asphyxia, is much more livid than in its natural state, the spleen also and the liver, when divided, emit only black blood, instead of that mixture of red and black blood which is observable, in the section of these organs, upon an animal which breathes freely.

But I trust that we have facts enough to establish it as a certainty, 1st, That the black blood after the interruption of the chemical functions of the lungs, continues for some time to circulate, and 2dly, That it penetrates into the organs, where it replaces the red blood; these circumstances explain the reason, why on opening the body we always meet with black blood even in the vessels which are destined for the circulation of arterial blood.

In the last moments of existence of whatever death the individual may have died, we shall always observe the lungs become embarrassed and cease to perform their office, for some time previous to the total suspension of the functions of the heart. The blood makes its circle through the system, after ceasing to receive the influence of the air, and consequently in its venous state; accordingly it must remain so in the organ in every case, although the circulation be much less evident, than in asphyxia, for it is in this circumstance that consists, the great peculiarity of asphyxia. The following phenomena may now be easily understood.

1st. When the left auricle and ventricle together with the large divisions of the aorta, on opening the body, are found to contain blood, such blood is always black. The fact is familiar to those who are in the habit of dissecting. In exercising my pupils on the surgical operations, I have always observed that when the open arteries are not entirely empty, their contents are composed of venous blood.