General Anatomy, Applied to Physiology and Medicine, Vol. 3 (of 3)

by Xavier Bichat

Extensibility is very evident in the organic muscles. The dilatation of the intestines and the stomach by aliments, by the extrication of gas, by the fluids that are found there, that of the bladder by the urine, by injections that are forced in, &c. are essentially owing to this extensibility.

This property is characterized here by two remarkable attributes; 1st, by the rapidity with which it can be put into action; 2d, by the very great extent of which it is susceptible.

The stomach and intestines pass in an instant from complete vacuity to great extension. Artificially distended, the bladder becomes immediately of a size treble, quadruple even of that which is natural to it. It sometimes however resists, but this does not prove its defect of extensibility; it is because the fluid injected irritates it and makes it contract; the organic contractility in exercise, then prevents the development of extensibility, as it sometimes cannot be brought into action by stimulants in a muscle laid bare, because the animal contractility in exercise in the muscle, forms an obstacle to it. The muscles of animal life are never capable of this rapidity in their extensibility, whether because they are intersected by numerous aponeuroses which dilate but slowly, or whether because their layers of fibres are very thick, two circumstances that do not exist in the muscles of organic life. Hence a remarkable phenomenon that I have observed in all cases of tympanites. When we open the abdomen of subjects that have died in this state, without wounding the swelled intestines, these immediately burst out, swell more, and occupy twice as large a space as they were contained in in the abdomen; why? Because the parietes of the abdomen being unable to yield in proportion to the quantity of gas that is developed, this has been compressed in the intestines during life, and expands immediately by its elasticity when the cause of compression ceases. In dropsies in which the distension is slow, the abdominal parietes enlarge much more than in tympanites. The size of the abdomen would be double in this, if the extensibility of the parietes was in proportion to that of the intestines.

As to the extent of the extensibility of the organic muscles, we can form an idea of it by comparing the empty stomach which oftentimes is not larger than the cæcum in its ordinary state, with the stomach containing sometimes five, six and even eight pints of fluid; the bladder contracted and concealed behind the pubis, with the bladder full of urine from suppression, rising sometimes even above the umbilicus; the rectum empty, with the rectum filling a part of the pelvis in old people in whom the excrements have accumulated in it; the intestines contracted with the intestines greatly distended.

It is to the extent of extensibility of the organic muscles and to the limits placed to that of the abdominal parietes, that must be referred a constant phenomenon that is observed in the gastric viscera; viz. that in the natural series of their functions, they are never all distended at the same time; the intestines are filled when the matters contained in the stomach are evacuated; the bladder is not full of urine in the digestive order, until the other hollow organs are empty, &c. In general, that is an unnatural order in which all the organs are distended at once.

There is for the organic muscles a mode of extensibility wholly different from that of which I have just spoken; it is that of the heart in aneurisms, and the womb in pregnancy. The first, for example, acquires a size double, treble even sometimes in its left side, and yet it increases at the same time in thickness. This size is not owing to distension, but to a preternatural growth. The aneurismatic heart is to the ordinary heart, what this is to the heart of the infant; it is nutrition that makes the difference and not distension; for whenever it is owing to this it diminishes in thickness as it increases in extent; there is no addition of substance. Besides the aneurismatic heart has not often the cause that distends it, for commonly in this case the mitral valves allow a free passage to the blood; whilst when they are ossified the left ventricle often remains in a natural state. Moreover, the slow progress of the formation of aneurism proves that it is a preternatural nutrition that has presided over this increase of the heart. You would in vain then empty this organ of the blood it contains, it would not contract and resume its dimensions, as the inflated intestine does which we puncture to allow the air to escape.

In the womb there are two causes of distension; 1st, the sinuses greatly developed; 2d, an addition of substance, a real momentary increase of the fibres of the organ which remains as thick and even more so than in the natural state. At the time of accouchement, the sinuses immediately flatten by the contraction of the fibres; hence the sudden contraction of the organ. But as on the one hand nutrition alone can remove by decomposition the substances added to the fibres to enlarge them, and as on the other, this function is exerted slowly, after the womb has undergone the sudden contraction owing to the flattening of its sinuses, it returns but gradually and at the end of some time to its ordinary size. Extensibility is not then brought into action in the womb filled by the fœtus, and in the aneurismatic heart; these organs really become at that time the seat of a more active nutrition; they grow preternaturally, as they have grown naturally with the other organs; but these do not then experience an analogous phenomenon, they become monstrous in comparison. The womb decreases, because the motion of decomposition naturally predominates over that of composition after accouchement, whilst it was the reverse before this period. The aneurismatic heart remains always so.

These dilatations of the heart should be carefully distinguished from those really produced by extensibility, as in the right auricle and ventricle for example, which are found full of blood at the moment of death, because the lungs which are weakened, not allowing it to pass through them, compel it to flow back to the place from which it came. There are but few hearts which do not exhibit in very various degrees, these dilatations, which we have the power in a living animal of increasing or diminishing at will, according to the kind of death we produce. Two hearts are hardly ever of the same size after death; many varieties are met with, and these depend more or less on the difficulties which the blood experiences in the last moments, in passing through the lungs. Hence why in the diseases of the heart, there is no standard by which we can compare the morbid size, especially if we examine the organ as a whole. In fact the distension of the right side can give it an aneurismatic appearance, and a size even greater than that of some aneurisms. If we examine the left side separately, the error is more easily proved, because this side is subject to less variations. But the principal difference consists in the thickness. The power of contraction appears to increase in proportion to this thickness, which arises from the substance added by nutrition. It is this power which produces the great beating that is felt under the ribs, the strength of the pulse, &c.

Contractility.

It is in proportion to extensibility. It is often brought into action in the ordinary state. It is in virtue of this property, that the stomach, the bladder, the intestines, &c. contract, and acquire a size so small compared to what they have when they are full. In general, there is no muscle of animal life, which is capable of such extreme contractions as those of organic life.