28 ABSORPTION. 



favouring the doctrine of venous absorption, it may be doubted whether in this inference, as 



because they are free from the objection which in so many other cases of physiology, we have 



must always attach to those operations, where not been misled by a mere nominal resem- 



any considerable degree of mechanical violence blance, and have applied the term capillary to 



has been employed. It may indeed be ob- the action of the lacteals, because it had been 



jected, that in these cases, the examination of used to denote their dimensions. Perhaps, 



the body did not take place at the proper point strictly speaking, there is scarcely a single cir- 



of time; that, in some instances, it was made cumstance, in which the action of the lacteals 



at too early a period, before the extraneous can be assimilated to that by which fluids are 



body had time to enter the lacteals, and, in taken up by capillary tubes. The structure 



other cases, not until it had left them, and had and consistence of the tube itself, the nature of 



been discharged from the thoracic duct into the the substance on which it is supposed to act, 



veins. But this contingency must be regarded and their relative situation, are all of them 



as rather a possible than a probable occurrence, more or less different from what occurs in the 



and it is obvious that if any considerable num- ordinary cases of capillary attraction. And if 



ber of experiments were performed, we can there is a difficulty with respect to the lacteals, 



scarcely suppose it to exist. where we have at least some indistinct evidence 



The conclusion that we are disposed to draw of the mechanical disposition of the parts, which 



from all the facts and arguments that have been may seem favourable to this hypothesis, in a 



brought forwards on the subject is in favour of much greater degree will it exist with respect 



the possibility of venous absorption, at least to the lymphatics, where we have nothing to 



under peculiar circumstances ; at the same time direct our opinion, except the analogy which 



that there are strong anatomical considerations, may be presumed to exist between the two spe- 



which would induce us to suppose, that in the cies of absorbent vessels. 



ordinary actions of the system, the function of In consequence of these difficulties, and of 



absorption is confined to the lacteals and the the supposed inadequacy of the mechanical 



lymphatics.* theory, many physiologists have had recourse 



. 3. Inquiry into the mode in which the ab- to a certain specific action of the vessels, and 



sorbents act. In entering upon this inquiry have conceived that the chyle was taken up by 



there are two distinct subjects which present a power, which has been supposed to be ana- 



themselves for our consideration ; we must first logous to an elective attraction between the 



ascertain by what means the substances that are vessel and the substance that is absorbed.* 



absorbed enter the mouths of the vessels, and, There are indeed many circumstances which 



in the second place, after they have entered the would appear to indicate, that a certain kind of 



mouths, how they are conveyed along the ves- selection is exercised by the mouths of the 



sels themselves. vessels, for, as far as we are capable of judging, 



With regard to the first of these points we when substances possessed of the same con- 

 may remark, that while there is so much uncer- sistence and physical properties are placed in 

 tainty respecting the anatomical and physio- contact with these mouths, some of them are 

 logical structure of the mouths of the lacteals, received, while others are rejected. But we 

 and still more, while we are completely igno- must remark, that the same objection may be 

 rant of that of the lymphatics, we cannot ex- urged against this as against the former expla- 

 pect to arrive at any definite conclusion con- nation, that the term elective, which is borrowed 

 cerning the mode of their action. We may, from the chemical relation of bodies to each 

 however, venture to say, that there is strong other, is perhaps as little applicable to the case 

 reason to believe, that the absorbents terminate under consideration as that of capillary, which 

 in very minute or capillary vessels, that have refers more to their mechanical action, 

 open mouths, and that these mouths are brought Discarding therefore all these analogical 

 into contact or close approximation with the illustrations, which are at least of doubtful 

 substances to be absorbed. Hence, by an ana- application, we may remark, that the lacteals 

 logy, which it must be acknowledged is some- ought to be regarded, like every other part of 

 what vague, the action of these minute vessels the animal frame, as vital organs, possessed of 

 has been referred to capillary attraction. But appropriate and specific powers ; that, in this 



instance, we are not able to refer to any general 



9 A summary of M. Magendie's experiments and principle the train of events now under con- 



s d p e n dUC a nd n hil S F C i P m ai rH ^ oS' M* P * v ct "deration, and that we must therefore be satis- 



seq. and his .Llem. t. n. zoo . . 24o ; on this subject c j -.1 i f 



see also Bichat, Anat. Gen. t. ii. 104, 5, with the hed Wllh sim p!y Stating the fact, that the lac- 

 remarks of Beclard, p. 130. We must not omit to teals nave ^ e power of taking up by their 

 notice the experiments of M. Segalas, who by extremities certain substances, with which they 

 dividing the bloodvessels of a portion of the intes- are in close approximation : that, for the most 



3fe53friS23; r> "* - b r h \ h the recei r a v he 



no absorption took place, and hence concludes that elem ents of the chyle, that they select these 

 the lacteals do not possess this power ; Magendie's fr m the contents of the intestinal canal, and 

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

 Franchini of Bologna thought that the lymphatics Physiol. t. ii. p. 397, 8 ; Young's Med. Lit. p. 112 ; 

 absorb " la sostanza assimilabile," but that the sub- Bell's Anat. v. iv. p. 290. M. Magendie, however, 

 stances which do not directly contribute to nutrition is disposed to reject all these hypothetical explana- 

 are absorbed by the veins j Consider. Fisiol. sull* tious ; Elem. t. ii. p. 162,3, and Journ. t. i. p. 3. 

 Assorb. p. 44. et alibi. 



