22 



ABSORPTION. 



frequently anastomose with each other, so as, 

 in many instances, to form a complete network 

 or plexus, in which respect their course differs 

 from that of the veins, where the small branches 

 unite to form the larger ones, without the lateral 

 communications. 



The lacteals are furnished with numerous 

 valves, which are disposed in pairs, and have 

 their convex surface turned towards the intes- 

 tine,* so that, in the ord.nary and healthy con- 

 dition of the vessels, their contents are pre- 

 vented from retrograding, and necessarily pro- 

 ceed from the small branches to the larger 

 trunks. The coats of the lacteals are thin and 

 transparent, and hence it is that these vessels, 

 except when they are filled with chyle, are so 

 difficult of detection. They seem, however, 

 notwithstanding the apparent delicacy of their 

 texture, to be possessed of considerable 

 strength, and to bear being distended far be- 

 yond their ordinary dimensions without being 

 ruptured. When they are completely filled 

 with chyle, and still more, when they are for- 

 cibly distended by injections, the number of 

 valves which they possess gives them a jointed 

 or knotted appearance, and it seems to have 

 been this circumstance, together with the white 

 colour of their contents, which first attracted 

 the notice of anatomists, and led to their dis- 

 covery. With respect to their structure, besides 

 the peritoneal covering which they possess in 

 common with all the abdominal viscera, they 

 seem to be composed of two distinct parts, an 

 internal membrane, which by its duplicature 

 forms the valves, and an external membrane, 

 which constitutes the main substance of the 

 vessel. 



To these two obvious component parts many 

 authors have added a muscular coat, and some 

 anatomists of great respectability assert that 

 they have actually detected transverse fibres, in 

 which their contractile power is supposed to 

 reside. Other anatomists, however, of equal 

 authority, deny the existence of this muscular 

 coat, and, it must be acknowledged, that the 

 weight of the negative evidence seems to pre- 

 ponderate. But we may remark, on the other 

 hand, that although these transverse fibres, 

 constituting the muscular coat, in consequence 

 of their transparency, or from some other 

 cause, have hitherto eluded our observation, 

 so that we have no positive proof of their 

 existence, the lacteals certainly exhibit what 

 appears to be very decided marks of contracti- 

 lity, and as they are not immediately con- 

 nected with any organ equivalent to the heart, 

 there seems to be no means, except their own 

 contractility, by which their contents can be 

 propelled-! See CHYLIFEROUS SYSTEM; LAC- 



* These were very minutely examined by Ruysch, 

 Dilucid. Valvul., op. t. i, p. 1 . . 13 ; they are ac- 

 curately described by Sheldon, p. 28. 



t Mascagni, ps. i. sect. 4. p, 26, informs us that 

 he could not detect the fibres; Cruikshank, on the 

 contrary, conceives that he has seen them in the 

 thoracic duct, p. 61 et alibi ; and Sheldon speaks 

 of the muscular coat as sufficiently obvious, p. 26. 

 Meckel, Manuel, (. i. p. 185, does not admit their 

 sxistence ; and this is the case with Chaussier and 



The anatomical structure of the lymphatics 

 seems to be essentially similar to that of the 

 lacteals ; they are composed of a firm elastic 

 membranous substance, capable of consider- 

 able distention without being ruptured, and 

 furnished with numerous valves ; like the lac- 

 teals they form very frequent anastomoses. 

 We have the same evidence of their contracti- 

 lity as of that of the lacteals, although we are 

 perhaps still less able to demonstrate the actual 

 existence of their muscular fibres. We presume 

 that they are likewise analogous to the lacteals 

 in the nature of their office, and in their desti- 

 nation, although they differ from them with 

 respect to their situation, or the parts of the 

 body to which they are attached ; the lacteals 

 being confined to the membranes connected 

 with the intestines, while the lymphatics are 

 found in almost every part of the body, and 

 connected with nearly all its various textures.* 

 They differ also in the nature of the fluid 

 which they contain, for while that of the lac- 

 teals, as has been stated above, is white and 

 opaque, the fluid found in the lymphatics is 

 transparent and colourless, so as to resemble 

 water, from which they have derived their spe- 

 cific denomination. 



It is very difficult, if not impossible, to trace 

 the actual commencement of the lymphatics ; 

 but partly from anatomical researches, and 

 partly from physiological considerations, we 

 are led to conclude that they originate from 

 the various surfaces of the body, of all de- 

 scriptions, both internal and external. They 

 resemble the lacteals, in passing from larger 

 to smaller branches, which, after numerous 

 anastomoses, unite in a few large trunks, the 

 greatest part of which terminate in the thoracic 

 duct. The great trunks of the lymphatics are, 

 for the most part, arranged into two distinct 

 series, one considerably more superficial than 

 the other; it is observed that they generally 

 follow the course of the great veins, but it may 

 be doubted whether any direct communication 



Adelon, " Lymphatique,"Dict. des Sc. Med. t.xxix. 

 p. 256. Breschet, art. " Lymphatique Systeme," 

 Diet, de Med. t. xiii. p. 389, considers it doubtful. 

 Some curious observations were made by Desge- 

 nettes, on the action of the absorbents after the 

 apparent death of the system, Journ. Med. t. Ixxxiv. 

 p. 499 et seq. Similar observations were after- 

 wards made by Valentin, t. Ixxxvi. p. 231, et seq. ; 

 this action was not, however, supposed to depend 

 on contractility. Wrisberg informs us that he has 

 frequently seen spasmodic contractions in the large 

 vessels a'nd in the thoracic duct, Observ. Anat. 

 Med. de Vas. Abs. Morb. in Comment. Soc. Reg. 

 Gotting. v. ix. 19. p. 149. 



* For the extent of the lymphatic system, see 

 Haller, El. Phys. ii. 3. 4, and the later account 

 of M. Magendie, Physiol. t. ii. p. 174, and Jour, 

 t. i. p. 3, who conceives that absorbent vessels have 

 not been detected in the brain, the spine, and the 

 organs of sense. Dr. Alison likewise conceives that 

 they have not been detected in the cranium or ner- 

 vous system, Outlines of Physiol. p. 76. Mas- 

 cagni, however, appears to have detected a few 

 small lymphatics in the brain, tab. 27. fig. 1. 

 Monro secundus argues in favour of their existence, 

 but it does not appear that he actually detected 

 them in any part of the nervous system ; on the 

 Nervous System, ch. v. sect 1. and Three Treatises, 

 ch. 4, 5. 



