3 o4 PROD UCTION AND ABSORPTION OF L YMPH. 
difference in composition exists between intra- and extravaseular fluids, 
so long will diffusion currents be set up tending to equalise this 
difference. 
Absorption of isotonic fluids. — These experiments, therefore, have 
no direct bearing on the absorption of lymph, i.e. the normal tissue 
juices. In this case the fluid to be absorbed resembles in almost all 
particulars the blood plasma, and possesses the same osmotic pressure 
as the latter, so that it would seem that there are no forces of diffusion 
or osmosis tending to absorption. Miiller 1 concludes from similar 
considerations that " the removal of collections of fluid must be effected 
in many cases by means of the lymphatics, independently of imbibi- 
tion into the capillaries." The mechanism of this lymphatic absorption 
has been already studied. We have now to inquire whether at any 
time fluids, such as those normally present in the tissues and isotonic 
with the blood, can be taken up by the blood vessels. 
We may arrange the experiments which have been made to decide 
this point under three headings — ■ 
1. In the first set, observations were made on the absorption of 
isotonic salt solutions and blood serum from the pleural and peritoneal 
cavities. Orlow, 2 working under Heidenhain's direction, found that 
such fluids were absorbed rapidly from the peritoneal cavities of living 
animals, while the lymph flow from a cannula placed in the thoracic 
duct showed no (or only slight) increase, in no way comparable to 
the amount of fluid absorbed. He concluded, therefore, that the 
absorption was effected by the blood vessels and was dependent on 
the vital activity of the cells lining the serous cavities or of the 
endothelial cells of the capillaries. Hamburger and Leathes con- 
firmed these results, but showed that they could not depend on any 
vital activity of the endothelial cells, since absorption took place with 
equal rapidity even when poisonous solutions of sodium fluoride were 
employed. 
The great objection to these experiments is that they do not prove 
conclusively absorption by the blood vessels. It is still possible that the 
fluids may have been taken up by the subserous lymphatic network and 
had not reached the thoracic duct during the experiment. This is an 
objection raised by Cohnstein, 3 who concludes from very similar experi- 
ments that these fluids are carried away solely by the lymphatics. It 
might be thought that this question could be easily decided by observing 
whether fluids were still absorbed from the serous cavities after ligature 
of both lymphatic ducts. I have made a number of experiments of this 
description, but have failed to get decisive results. It is true that, after 
ligature of both thoracic ducts as well as of the right innominate vein, 
isotonic salt solutions were taken up fairly quickly from the serous 
cavities. In none of these cases, however, could I be certain that the 
lymph was absolutely shut off from the blood. As a rule I injected 
on three succeeding days several hundred c.c. saline solution into the 
peritoneal cavity, the last injection containing carmine granules in 
suspension. On killing the dog two days after the last injection, the 
peritoneal cavity was generally found to be empty, and carmine granules 
could be traced along the glands of the anterior mediastinum, showing 
that, in spite of the ligature of both lymphatic ducts, there had been a 
1 Loc. clt. 2 Arch.f. d. ges. Fhysiol., Bonn, 1S94, Bd. lix. S. 170. 
3 Centralbl. f. Fhysiol., Leipzig u. "Wien, 1895, Bd. ix. 
