ABSORPTION. 



31 



the experiments is totally different from any 

 thing to which the parts are exposed under 

 ordinary circumstances. It may be further 

 remarked, that if the texture of the vessels is so 

 permeable to fluids of all kinds and in all 

 directions, it is difficult to conceive of any 

 cause which can retain them there when they 

 have entered, and which should prevent their 

 escaping through the same pores when any 

 pressure is made on the contents of the vessels 

 by its contractile power or by any extraneous 

 force. 



And it may be further remarked concerning 

 these experiments, without impugning the accu- 

 racy or the dexterity of the operator, that they 

 imply a degree of minuteness in the execution, 

 and of attention to a variety of concurrent cir- 

 cumstances, and are altogether of so extremely 

 delicate a nature, as to render it undesirable that 

 any physiological conclusion should be founded 

 on them. If a single bloodvessel be divided, 

 however minute, and its extremity be exposed, 

 or even if a single cell of the membranous 

 texture be laid open, so as to admit of the 

 introduction of the fluid, the essence of the 

 experiment is destroyed, and its results must 

 become equivocal. 



Another hypothesis respecting the nature of 

 absorption has been lately brought forward by 

 Sir D. Barry, according to which it immediately 

 depends on atmospheric pressure, either ex- 

 ercised directly on the surface of the body, or 

 acting indirectly on the absorbents through the 

 medium of the great internal cavities. The 

 experiments on which the hypothesis rests con- 

 sisted in introducing a portion of some poison- 

 ous substance into a wound, and forming a 

 vacuum over it by means of a cupping-glass; 

 when, by contrasting the effect of the poison in 

 this case with that which ensues from the same 

 application where the cupping-glass was not 

 employed, he concludes that the process of ab- 

 sorption was suspended by removing the at- 

 mospheric pressure, and he hence infers that 

 this pressure is the cause of absorption.* 



The results of these experiments, in a prac- 

 tical point of view, are of great interest, but 

 with respect to the physiological conclusion that 

 has been drawn from them, there are various 

 circumstances to be taken into account, which 

 appear not to have been duly attended to. 



In the first place, a similar kind of objection 

 occurs in this case as in the experiments of 

 MM. Magendie and Deli lie related above, that 

 the poison was introduced into a wounded 

 part, and would therefore be immediately mixed 

 with the blood and carried into the general 

 circulation. The effect of a vacuum formed 

 over the divided extremity of a vessel, must be 

 to retard the progress of its contents, whatever 

 be its description, or in whatever cause it ori- 

 ginates. This effect is therefore not specifically 

 applicable to absorption, even in the natural 

 state of the parts ; and when we consider that 

 in this case there was an artificial opening 



' Barry's Exper. Researches, pt. 2 " On Ab- 

 sorption -," Alison's Outlines, p. 85 j Bostock's Phy- 

 siol. v. ii. p. 593 et seq. 



made into the vessel, we may venture to affirm 

 that the conclusion which was drawn from it is 

 in no respect the necessary inference from the 

 facts. 



And besides this general objection, it may be 

 fairly questioned how far the removal of pres- 

 sure from the surface of the body could act in 

 retarding the progress of a fluid along a vessel 

 which has no external opening, and which is 

 provided with valves, such as is strictly the 

 case with the lacteals, and may be almost said 

 to be so with the lymphatics. And with re- 

 spect to the lacteals, it appears a very obvious 

 objection to the hypothesis, that they are alto- 

 gether defended from the effects of atmospheric 

 pressure, either as applied directly, or as in- 

 directly acting on them through the medium of 

 any of the internal cavities. Besides, we have 

 sufficient proof of the spontaneous and inde- 

 pendent action of these vessels, whatever may 

 be our opinion respecting the existence of their 

 muscular coat, and to whatever principle we 

 may refer this action, and we have thus an 

 actual cause for the propulsion of their con- 

 tents, although it is impossible to estimate its 

 actual amount, it would appear unnecessary to 

 search for any farther agent, unless we have 

 good ground for concluding that the existing 

 cause is inadequate to produce the effect re- 

 quired. 



Cutaneous absorption. There is a branch 

 of the subject to which we must now direct 

 our inquiry, the existence and extent of what 

 has been termed cutaneous absorption. When 

 we trace the progress of the lymphatic vessels 

 from their great central trunks, and follow them 

 through all their minute ramifications, we find 

 that many of them appear to have their origin 

 from the surface of the body,* and hence we 

 are led to suppose that the function of ab- 

 sorption is exercised, to a certain extent, by the 

 cutis, or the parts immediately connected with 

 it. That this is the case is proved by various 

 pathological facts; we have daily opportunities 

 of observing, that various medicinal substances, 

 by mere application to the surface, and still 

 more when aided by friction, produce the same 

 effect upon the system as if they had been 

 received, in the ordinary way, through the 

 medium of the stomach. By this means 

 mercury manifests its specific action on the 

 salivary glands, the salts of lead destroy the 

 contractility of the muscular fibre, while opium, 

 tobacco, and other narcotics produce their pe- 

 culiar effects on the nervous system. 



But, besides this kind of absorption, which 

 is brought about by the substances being, as it 

 were, mechanically forced into the pores of the 

 skin, and thus applied to the mouths of the 

 lymphatics, it was an opinion very generally 

 embraced by the older physiologists, and still 

 retained by many of our contemporaries, that 

 the lymphatics, which are distributed over the 

 surface, possess the power of imbibing water, 

 when simply applied to it by the immersion 

 of the body, or even when it is exposed to 



* See Haase, De Vas. Cut. et Intest. Absorb., 

 tab. fig. 2j also, Mascagni, tab. 2. fig. 9. .28, tab. 3. 



