THEORY OF L UD WIG. 287 



transudation of water carrying solids in solution, the solids being taken 

 up by the tissues, and the pure water which is left over returned by 

 the lymphatics to the blood. We get here the first conception of the 

 irrigation theory of tissue nutrition which has played so great a part in 

 the speculations of later physiologists. 



With Hunter l and Monro 9 > we find a return to the older theory, that 

 lymph was produced by a process of suction. This indefinite conception, 

 however, allowed a considerable degree of individual licence as to the 

 details of the process, and important authors, such as Hunter and 

 Mascagni, 3 recognised the possibility of a simple transudation or filtra- 

 tion through the blood-vessel walls. This latter view, however, did not 

 meet with general recognition, physiologists preferring to believe 

 in the existence of the exhalant arteries which no one had yet seen 

 or was ever going to see. Thus we find Bichat 4 definitely asserting 

 the existence of " vasa exhalantia." Speaking of connective tissues, he 

 writes : " Chaque cellule du tissue cellulaire est un reservoir inter- 

 mediare aux exhalants, qui s'y terminent, et aux. absorbants qui en 

 naissent." The absorption through the supposed open mouths of the 

 lymphatic and lacteal vessels was attributed by most authorities of this 

 time to capillary attraction, while the onward flow of the fluid in the 

 lymphatics could, according to Cruickshank, only be explained as due 

 to the vital activity of living cells or tissues. Haller describes the 

 movement of the chyle from the intestines in exactly the same manner. 

 Particularly ingenious is Hewson's 5 explanation of the absorption and 

 movement of chyle in theTacteals. He shows that during life the blood 

 vessels of the villi and in the papillae of the skin and mucous mem- 

 brane, by their turgescence, keep the orifices of the lacteals or the similar 

 openings of the lymphatics patent, so that these are now capable of 

 attracting like capillary tubes made of hard substances. The further 

 movement of the chyle and lymph he ascribes to the peristaltic con- 

 traction of muscular fibres in the walls of the lacteals or lymphatics. 



Views very similar to these were held by some of the most dis- 

 tinguished of subsequent physiologists, such as Prochaska, Fohmann, 

 Burdach and Henle. In opposition to this mechanical theory of lymph 

 formation, Johannes Miiller, 6 having regard to the apparent power of 

 choice possessed by the lacteals, some substances being absorbed while 

 others were left, was inclined to ascribe at any rate the act of absorption 

 to the vital activities of the Living cells of the body. 



On the discovery of endosmosis by Dutrochet, 7 many physiologists 

 believed that at last the riddle of absorption and secretion of lymph was 

 solved, and from this time onwards we find an invocation, generally 

 more or less vague, of osmotic action to explain the phenomena of 

 absorption and secretion. 



Theory of Ludwig. The beginning of the new era in the history 

 of the physiology of lymph formation is marked by the important 

 paper of Ludwig and Noll. 8 In consequence of experiments on 



1 Works, edited by Palmer, London, 1835, vol. iv. p. 299. 



2 ' De venis lymphaticis valvulosis," 1757. 



Vasorum lymphaticorum corporis human! historia et iconographia," 1787. 

 Anatomie ge"ne"rale," 1812. 



A Description of the Lymphatic System, etc.," Collected Works, Syd. 8oc., 1846. 

 Elements of Physiology," Baly's trans., 1838, vol. i. p. 248. 



7 Previous article, p. 273. See also "Cyclopaedia of Anat. and Phys.," art. " Endosmose." 



8 Ztschr.f. rat. Mod., 1850, Bd. ix. S. 52. 



