ANATOMY.
The admission of matter into the orifices of the absorbing vessels has been accounted for in various ways. Some physiologists consider it as a case of capillary attraction. But a little re flection is sufficient to shew that the absorbents are not like capillary tubes immersed in a fluid. Besides, were such attraction the cause of absorp tion, that process should be carried on with regularity. On the contrary, absorp tion is occasionally very deficient, when abundance of fluids is presented to the mouths of the vessels, as in oedema ; and in other cases, after being for a long time inactive, it is suddenly exerted to a great extent ; thus large abscesses have been dispersed in one night. Others have en deavoured to discover some propelling power which should protrude the matter subject to absorption into the mouths of the vessels. The pressure of the atmos phere on the surface of the body has been considered adequate to this effect, and the deposition of new matter by the se cerning artery has been assigned as the use of the propulsion of the old parti ides into the orifice of the absorbent. On this theory, secretion and absorption should correspond more exactly than they are known to do. Mr..1. Hunter acknow ledged that he was unable to account for the effects produced, unless by attribut ing to the mouths of the absorbing ves sels powers similar to those which a ca terpillar exerts when feeding on a leaf.
Some suppose that the absorbents can not take up any matter that is not fluid; consequently, that animal solids must be converted into fluids before they can be come fit subjects for absorption ; and that probably some solvent fluid is secreted for this purpose. The latter fact rests on no direct proof, and the whole hypothe sis is very unlike the simplicity observa ble in other parts of the animal economy. It seems better, in these difficult investi gations, to note facts, than to form theo ries ; and whoever contemplates the things done in the animal body, will be astonished at the power of the vessels, by whose agency they must be effected ; a whole bone may perish, as, for example, that of the thigh, and may be increased by a new one ; the vascular lining of the new bone will altogether remove the dead one.
Besides the great and leading office of the absorbents in conveying the chyle into the venous system, their agency is discerned in various other parts of the animal economy. The nearly transparent fluid that lubricates the interstices of the cellular substance, and the serous exha lation poured into circumscribed cavities, are taken up by the lymphatics, which i must commence in all parts of the body by open orifices. When the due balance does not exist between the absorbing and secreting vessels, the cellular substance becomes loaded with fluid (anasarca), or circumscribed cavities are rendered drop sical. Together with the lymph or fluid which the absorbing vessels derive from the sources just mentioned, they convey from every part of the body the old con stituent materials of our organs, in pro portion as new particles are deposited by the arteries ; and these different elements are intimately mingled and combined in their passage through the absorbent glands, and the plexures of lymphatic vessels.
It has been a disputed point whether absorption goes on from the surface of the skin, while the cuticle is entire ; the arguments on the affirmative sides are an alleged increase of weight in the body after a walk in damp weather ; the abun dant secretion of urine after remaining for some time in a bath ; the evident swell ing of the inguinal glands after a long immersion of the lower extremities in warm water ; the effects of mercury ad ministered by friction, fumigation, &c. It has been stated in opposition, that oil of turpentine has not been absorbed after long immersion of the arm ; that solutions of medicated substances have not been taken up under similar circumstances, &c. We think it is sufficiently proved, that absorption from the surface does take place in the human body, but whether this extends, as a modern physiologist has stated, to gaseous bodies, cannot yet be decided.