302 PROD UCTION AND ABSORPTION OF L YMPH. 



No such mechanism exists in the mammalia. Heller and Colin 

 have observed rhythmic contractions of the lacteals in the mesentery, 

 but only in the herbivora. In the case of the chyle vessels, Briicke l has 

 shown that the onward flow of lymph is helped by the rhythmic con- 

 tractions of the muscular fibres of the intestinal villi, which empty the 

 central cavity of the villus into the underlying network of lymphatics. 



Since the walls of most lymphatic vessels and of the thoracic duct 

 are provided with unstriated muscular fibres, we should expect these 

 vessels to be constricted, in consequence of direct stimulation, and such 

 constrictions have been observed in executed criminals. It has been 

 shown more recently that' an active contraction or dilatation of the 

 lymphatics can be brought about by electrical stimulation of certain 

 nerves. Thus Paul Bert and Laffont ' 2 noticed contraction of the 

 lacteals on stimulation of the mesenteric nerves, and a dilatation of the 

 same vessels on exciting the splanchnics. Gley and Camus 3 have 

 lately repeated these experiments more carefully, and have obtained 

 graphic evidence of a dilatation of the cisterna lymphatica on stimula- 

 tion of the splanchnic nerve. This dilatation of the cisterna probably 

 explains the temporary stoppage in the lymph flow from the thoracic 

 duct which I described as the immediate effect of splanchnic stimulation. 



It is probable, however, that the active contractility of the walls of 

 the lymphatics is of very little importance for the flow of lymph 

 through them. The only factors which are of importance are mechanical, 

 and are 



1. The pressure under which the lymph is poured into the tissue 

 spaces. This in its turn is dependent on the differences of pressure 

 between the intra- and extracapillary fluids, as well as on the per- 

 meability of the vessel walls. 



2. All the muscular contractions of the body, and especially those 

 by which the respiratory movements are carried out. 



THE ABSORPTION OF LYMPH FROM THE CONNECTIVE TISSUES. 



Relative importance of blood vessels and lymphatics. Before 

 the discovery of the lacteals by Asellius, anatomists ascribed the office 

 of absorption generally to the veins. From this time until the begin- 

 ning of the present century, no subject was more hotly disputed than 

 the question of the relative importance of the veins and of lymphatics 

 in the processes of absorption. 



It was generally conceded that the lacteals performed practically 

 the whole work of absorbing the products of digestion from the intes- 

 tines ; but the views as to the functions of the other lymphatics of the 

 body were many and various. Thus, when Nuck 4 first made his 

 experiments, in which he thought he injected these lymphatics from the 

 arteries, he concluded that they had no other use than as correspondent 

 veins, to return the lymph from such arteries as were too small to admit 

 the red blood corpuscles. As anatomical and clinical knowledge increased, 

 it was gradually recognised that the general lymphatics of the body had 

 a function similar to that of the lacteals in the intestines, and like them 



1 "Ueber die Chylusgefasse und Fortbewegung des Chylus," Wien, 1853. 



2 CompL rend. Acad. d. sc., Paris, March 13, 1872. 



3 "Recherches dans les causes de la circulation lymph atique," Diss., Paris, 1894. 



4 " Adenographia curiosa, " Leidse, 1691. 



