ABSORPTION FROM THE BODY IN GENERAL. 445 



the rate of endosmotic absorption, is easily proved experimentally; and this it 

 is which constitutes the main difference between the living and the dead subject. 1 



465. It is a very remarkable fact, which has recently been fully substantiated, 

 that not merely soluble matters, but insoluble substances in a state of minute 

 division, may find their way from the alimentary canal into the current of the 

 circulation. Thus it was found by Oesterlen 3 that particles of finely-divided 

 charcoal, introduced into the alimentary canal, could be distinguished in the 

 blood of the mesenteric veins ; and similar results have been obtained by Eber- 

 hard, and by Mensonides and Bonders, not only with charcoal, but also with 

 sulphur, and even with starch, the latter substance being at once detectible in 

 the blood by the iodine-test. It is doubtful whether these particles are taken 

 up by the lacteal system; though Bonders seems of opinion, from finding them 

 deposited in the lungs rather than in the liver, that the former is their more 

 usual channel of entrance. 3 How they find their way through the walls of the 

 vessel, however, is at present a complete mystery. 



2. Absorption from the Body in general. 



466. The Mucous Membrane of the alimentary canal is by no means the only 

 channel through which nutritive or other substances may be introduced into the 

 circulating apparatus from external sources. The Lymphatic system is present 

 in all animals which have a lacteal system ; and the two, as already pointed 

 out, evidently constitute one set of vessels. The Lymphatics, however, instead 

 of commencing on the intestinal walls, are distributed through most of the vas- 

 cular tissues of the body, and especially in the Skin; but their number bears 

 no proportion whatever to the vascularity of the several tissues, or to the amount 

 of interstitial change which these undergo; and it is remarkable that the Nerv- 

 ous centres should be (so far as is yet known) entirely destitute of them, and 

 that they should be so scanty in the interior of Muscles, as to suggest that they 

 belong rather to the connective areolar tissue than to the muscular substance 

 itself (308). Their origins cannot be clearly traced; but they seem in general 

 to form a plexus in the substance of the tissues, from which the convergent 

 trunks arise. After passing, like the lacteals, through a series of glandular 

 bodies (the precise nature of which will be presently considered, 473), they 

 empty their contents into the same receptacle with the lacteals ; and the mingled 

 products of both pass into the Sanguiferous system. We find in the Skin, also, 

 a most copious distribution of capillary bloodvessels, the arrangement of which 

 is by no means unlike that of the bloodvessels of the alimentary canal; and its 

 surface is further extended by the elevations that form the sensory papillae (Fig. 

 115), which are in many points comparable to the intestinal villi, although their 

 special function is so different. 



467. In the lowest tribes of animals, and in the earliest condition of the 

 higher, it would seem as if Absorption by the external surface is almost equally 

 important to the maintenance of life, with that which takes place through the 

 internal reflexion of it forming the walls of the Digestive cavity. In the adult 

 condition of most of the higher animals, however, the special function of the 

 latter is so much exalted, as usually to supersede the necessity of any other 



he had found albumen in the duodenum. On this fact Dr. Prout much relied as a proof 

 of the convertibility of starch into albumen an idea which would now be universally con- 

 demned by Organic Chemists ; but it does not seem difficult to believe, that the presence 

 of a viscid mass of half-digested starch might have determined a transudation of albumen 

 from the bloodvessels by endosmosis. 



1 On the whole of this subject, see the Author's "Princ. of Phys., Gen. and Comp.," 

 CHAP. xi. Am. Ed. 



2 "Heller's Archiv.," 1847. 3 "Henle's Zeitschrift," 1851, 



