3 o2 PROD UCTION AND ABSORPTION OF L 1 'MPH. 
No such mechanism exists in the mammalia. Heller and Colin 
have observed rhythmic contractions of the lacteals in the mesentery, 
hut only in the herbivora. In the case of the chyle vessels, Briicke 2 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 tin night 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 Cliylus," Wien, 1853. 
- Cornpt. rend, Acad. d. sc, Paris, March 13, 1872. 
3 "Reoherches dans les causes de la circulation lymphatique," Diss., Paris, 1894. 
4 " Adenograpliia curiosa," Leidse, 1691. 
