As to organic sensibility, it evidently exists in the arteries, since it cannot be separated from the preceding contractility; like it, it is obscure in the great trunks, which have only what is necessary for their nutrition.
From the small development of the organic forces of the arterial texture, it is evident that this texture would rarely be the seat of affections, over which these properties particularly preside. This also is proved by observation.
1st. Acute diseases are rarely observed in the arteries. Among all the bodies that I have examined, I have found but very few in which there were traces of inflammation in the arterial texture. I would observe upon this subject, that it is necessary to distinguish accurately the redness which is, as we have said, the effect of maceration, and which even appears spontaneously in the dead body some time after death, especially in the cerebral arteries; it is necessary, I say, to distinguish it from that which arises from inflammation. In one the arterial fibres are really red, in the other they appear so only by the injection of their vessels. Is the common membrane inflamed in inflammatory fever? I am entirely ignorant. These simple fevers are so rare, especially in hospitals that we have hardly an opportunity of examining patients that have died of them. But by supposing that this inflammation existed, the infrequency of these fevers considered in their simple state, would prove even how little the arteries are disposed to inflame. 2d. The arteries are not often the seat of chronic affections. Except on the one hand aneurism, in which the arterial texture is hardly altered, but merely broken, and in which consequently its organic sensibility performs but a very small part; on the other, the osseous incrustations, most of the alterations that are so frequent in the other textures, are not observed in this.
This texture must be ranked with the cartilaginous, the fibro-cartilaginous, the fibrous, the muscular even, &c. as it respects the infrequency of organic alterations. These textures exhibit a phenomenon opposed to that of the serous, mucous, glandular, dermoid systems, &c. which are especially characterized by the frequency of these alterations. Compare the organic properties, the sensibility and insensible contractility in the two classes of textures; you will see them very feeble in the first, in which in a natural state, they preside only over nutrition; you will observe, on the contrary, that they are very evident in the second, because there they preside over nutrition, exhalation, absorption, secretion, &c.
The difficulty with which the arterial texture inflames and participates in the different alterations of the neighbouring organs, preserves the integrity of the circulation in many cases. What would become of this function, if the arteries received as easily as the other textures, the influence of surrounding diseases? Placed at every moment by the side of inflamed, suppurating, swelled parts, &c. if they become changed by their neighbourhood, especially in the great trunks, a general derangement would soon be felt in the motion of the blood. Dissect the arteries in the organic affections of the stomach, the liver, the spleen, &c.; they are untouched, and only a little increased in size; whilst a general swelling seems to confound in a new mass all the neighbouring textures.
The clots in aneurism adhere sometimes so intimately to the common membrane, that we are obliged to remove them with an instrument. But this adhesion is entirely inorganic; it is a kind of agglutination, that would imply the small degree of life of this common membrane, as the facility with which colours are fixed in the epidermis implies it in this last organ.
Remarks upon the causes of the motion of the red blood.
The red blood is moved in the heart by a mechanism which there is no difficulty in understanding. But an important question remains to be decided concerning its motion in the arteries; are these vessels active or passive in this motion? When the physician examines the different states of the pulse, is it the state of the heart or that of the arterial system that he ascertains? From the absence of sensible organic contractility, as we have observed in this texture, it is evident that its part would be especially passive; that the motion of which it is the seat is communicated to it; that the heart is the great agent of the pulsation of the arteries; that it is that which gives the impulse, which these vessels only obey, and that consequently in almost all cases the state of the pulse is the index of the state in which the vital forces of the heart are found, and not of the state of the arterial system, whose life is not more raised in the greatest and most frequent pulsatory motions, than in the feeblest and most infrequent. Thus in convulsions, the principle of which is a wound, an irritation of the brain, &c. the nerves, though conductors, are, if we may so say, passive.
I will now examine in detail this important question, that so many physicians have considered differently.