TILITY.) II. The tissues of the animal body are pos sessed of very various degrees of elasticity; some of them are but little inferior to the most highly elastic unorganized substances, while others are endowed with this property in so very trifling a degree, that in our physiological and pathological reasonings concerning them, we may almost consider it as absent. We shall endeavour to arrange the principal organic tissues in the order of their elasticity, and shall then proceed to offer a few remarks upon each.
I. Yellow fibrous tissue. 2. Cartilage. 3. Fibro-cartilage. 4. Skin. 5. Cellular mem brane. 6. Muscle. 7. Bone. 8. Mucous membrane. 9. Serous membrane. 10. Ner vous matter. 11. Fibrous membrane.
This view of the comparative elasticity of the different tissues must not be regarded as rigorously exact : owing to the impossibility of procuring each one perfectly separate from the others, the result of our experiments can be considered merely as approximate.
I. The yellow fibrous system.—The tissues composing this system are unquestionably the most highly elastic of all : the ligaments sub flava which unite the laminae of the vertebra: to one another, and the ligamentum nuchm which suspends the head io some of the larger quadrupeds, are scarcely inferior to caoutchouc In this respect. The middle coat of arteries is referred by Beclard to the yellow fibrous system, perhaps from its possessing in so high a degree this characteristic property. Its exis tence may be demonstrated by various experi ments, and many of the physiological and pathological phenomena of the arterial tissue are modified or determined by its presence. The sudden expansion of an artery whether in the living or dead body upon the removal of a force pressing its sides together; the gradual contraction of a divided artery, by means of which hemorrhage is so frequently arrested ; the contraction or obliteration of the vessel beyond the ligature, after it has been taken up in aneurism ; the obliteration of the umbilical arteries and of the ductus arteriosus soon after birth ; the gaping which occurs in longitudinal wounds of arteries owing to the recession of the divided edges; the power possessed by these vessels of accommodating their size to the quantity of circulating blood, (thus causing endless variations in the volume of the pulse even in the same individual) ;—all these facts have been accounted for by the transverse elasticity of the middle coat. The effects of
this property in a longitudinal direction may be seen in the retraction of divided arteries during amputation ; in the sort of locomotion which these vessels undergo from the impulse of the blood, and in the enlargement of a transverse arterial wound by the retraction of its edges. The proper coat of veins, though belonging likewise to this system, is however much less elastic than that of the arteries ; but we cannot agree with those who deny this property to the venous tissue. The sudden flow of blood from a portion of vein included between two ligatures ; the constantly varying size of the cutaneous veins according to the volume of their contents; the obliteration under certain circumstances of veins where circulation has been arrested, appear to us explicable only by attributing this property to them.
2. Cartilage is possessed of very great elas ticity. On pressing the point of a scalpel into cartilage it is expelled upon the suspension of the force by the contraction of the sur rounding substance. It may also be well de monstrated by twisting or bending the carti lages of the ribs, or those of the nose, eyelid, &c. The elasticity of cartilage in the adult is much greater than in the child or old person. 'We shall allude presently to the several impor tant objects to which this property as connected with cartilage is applied.
3. Fibro-eartilage.—The elasticity of this tissue may be studied in the intervertebral fibro-cartilages, in which it contributes so remarkably to the obscure movements of the spinal column and to the security of the chord : it is remarkably displayed in restoring the sub stance to its proper condition, when pressure rather than twisting or bending has been the cause of derangement. The fibro-cartilaginous funnels through which the tendons are trans mitted, possess likewise this property to a great extent. Bichat found, on removing a tendon in a living dog, that the funnel through which it had been transmitted became impervious, like an artery under similar circumstances.