28 



ABSORPTION. 



favouring the doctrine of venous absorption, 

 because they are free from the objection which 

 must always attach to those operations, where 

 any considerable degree of mechanical violence 

 has been employed. It may indeed be ob- 

 jected, that in these cases, the examination of 

 the body did not take place at the proper point 

 of time; that, in some instances, it was made 

 at too early a period, before the extraneous 

 body had time to enter the lacteals, and, in 

 other cases, not until it had left them, and had 

 been discharged from the thoracic duct into the 

 veins. But this contingency must be regarded 

 as rather a possible than a probable occurrence, 

 and it is obvious that if any considerable num- 

 ber of experiments were performed, we can 

 scarcely suppose it to exist. 



The conclusion that we are disposed to draw 

 from all the facts and arguments that have been 

 brought forwards on the subject is in favour of 

 the possibility of venous absorption, at least 

 under peculiar circumstances ; at the same time 

 that there are strong anatomical considerations, 

 which would induce us to suppose, that in the 

 ordinary actions of the system, the function of 

 absorption is confined to the lacteals and the 

 lymphatics.* 



. 3. Inquiry into the mode in which the ab- 

 sorbents act. In entering upon this inquiry 

 there are two distinct subjects which present 

 themselves for our consideration ; we must first 

 ascertain by what means the substances that are 

 absorbed enter the mouths of the vessels, and, 

 in the second place, after they have entered the 

 mouths, how they are conveyed along the ves- 

 sels themselves. 



With regard to the first of these points we 

 may remark, that while there is so much uncer- 

 tainty respecting the anatomical and physio- 

 logical structure of the mouths of the lacteals, 

 and still more, while we are completely igno- 

 rant of that of the lymphatics, we cannot ex- 

 pect to arrive at any definite conclusion con- 

 cerning the mode of their action. We may, 

 however, venture to say, that there is strong 

 reason to believe, that the absorbents terminate 

 in very minute or capillary vessels, that have 

 open mouths, and that these mouths are brought 

 into contact or close approximation with the 

 substances to be absorbed. Hence, by an ana- 

 logy, which it must be acknowledged is some- 

 what vague, the action of these minute vessels 

 has been referred to capillary attraction. But 



* A summary of M. Magendie's experiments and 

 deductions is contained in his Journ. t. i. p. 18 et 

 seq. and his Elem. t. ii. 238 . .243 ; on this subject 

 see also Bichat, Anat. Gen. t. ii. 104, 5, with the 

 remarks of Beclard, p. 130. We must not omit to 

 notice the experiments of M. Segalas, who by 

 dividing the bloodvessels of a portion of the intes- 

 tine, and leaving the lacteals, thus, as it were, re- 

 versing the experiments of M. Magendie, found that 

 no absorption took place, and hence concludes that 

 the lacteals do not possess this power ; Magendie's 

 Journal, t. ii. p. 117 et seq. So singular a conclu- 

 sion must, we conceive, lead us to place but little con- 

 fidence in the result of such complicated experiments. 

 Franchini of Bologna thought that the lymphatics 

 absorb " la sostanza assimilabile," but that the sub- 

 stances which do not directly contribute to nutrition 

 are absorbed by the veins j Consider. Fisiol. sull' 

 Assorb. p. 44. 



it may be doubted whether in this inference, as 

 in so many other cases of physiology, we have 

 not been misled by a mere nominal resem- 

 blance, and have applied the term capillary to 

 the action of the lacteals, because it had been 

 used to denote their dimensions. Perhaps, 

 strictly speaking, there is scarcely a single cir- 

 cumstance, in which the action of the lacteals 

 can be assimilated to that by which fluids are 

 taken up by capillary tubes. The structure 

 and consistence of the tube itself, the nature of 

 the substance on which it is supposed to act, 

 and their relative situation, are all of them 

 more or less different from what occurs in the 

 ordinary cases of capillary attraction. And if 

 there is a difficulty with respect to the lacteals, 

 where we have at least some indistinct evidence 

 of the mechanical disposition of the parts, which 

 may seem favourable to this hypothesis, in a 

 much greater degree will it exist with respect 

 to the lymphatics, where we have nothing to 

 direct our opinion, except the analogy which 

 may be presumed to exist between the two spe- 

 cies of absorbent vessels. 



In consequence of these difficulties, and of 

 the supposed inadequacy of the mechanical 

 theory, many physiologists have had recourse 

 to a certain specific action of the vessels, and 

 have conceived that the chyle was taken up by 

 a power, which has been supposed to be ana- 

 logous to an elective attraction between the 

 vessel and the substance that is absorbed.* 

 There are indeed many circumstances which 

 would appear to indicate, that a certain kind of 

 selection is exercised by the mouths of the 

 vessels, for, as far as we are capable of judging, 

 when substances possessed of the same con- 

 sistence and physical properties are placed in 

 contact with these mouths, some of them are 

 received, while others are rejected. But we 

 must remark, that the same objection may be 

 urged against this as against the former expla- 

 nation, that the term elective, which is borrowed 

 from the chemical relation of bodies to each 

 other, is perhaps as little applicable to the case 

 under consideration as that of capillary, which 

 refers more to their mechanical action. 



Discarding therefore all these analogical 

 illustrations, which are at least of doubtful 

 application, we may remark, that the lacteals 

 ought to be regarded, like every other part of 

 the animal frame, as vital organs, possessed of 

 appropriate and specific powers ; that, in this 

 instance, we are not able to refer to any general 

 principle the train of events now under con- 

 sideration, and that we must therefore be satis- 

 fied with simply stating the fact, that the lac- 

 teals have the power of taking up by their 

 extremities certain substances, with which they 

 are in close approximation ; that, for the most 

 part, the substances which they receive are the 

 elements of the chyle, that they select these 

 from the contents of the intestinal canal, and 



* See Bichat, Anat. Gen. t. ii. p. 125; Dumas, 

 Physiol. t. ii. p. 397, 8 ; Young's Med. Lit. p. 112 ; 

 Bell's Anat. v. iv. p. 290. M. Magendie, however, 

 is disposed to reject all these hypothetical explana- 

 tions ; Elem^t. ii. p. 162,3, and Journ. t. i. p. 3. 

 et alibi. 



