CARL LUDWIG. 173 



presence of the valves in the lymphatics, to conclude that 

 the natural path for the lymph and therefore other fluids to 

 pass in these vessels was from periphery to centre, and so 

 he hit upon the apparently simple yet really scientific method 

 of injecting these vessels with a watery solution of Berlin 

 blue, the nozzle of a fine hypodermic syringe being thrust 

 under or into the skin or other organ, when lymphatics are 

 immediately filled with the blue fluid. Indeed it is a most 

 beautiful and instructive experiment to show the lymphatics 

 in the limb of a dead animal by this method. In this 

 way these observers were able to study the distribution 

 of lymphatics in fasciae and tendons, and to show how im- 

 portant are movements for the onward flow of the lymph, 

 a view that was confirmed by the experiments of Genersich, 

 Lesser, Emminghaus, and others on the effect of movements 

 — active and passive — on lymph flow. Ludwig was con- 

 tinually striving to arrive at a correct knowledge of the 

 relation of the tissue elements to the lymphatics on the one 

 hand, and the blood-vessels on the other. Numerous ex- 

 periments led him to formulate the filtration hypothesis re- 

 garding the formation of lymph, an hypothesis which is still 

 sub judice, and is even to-day the subject of lively contro- 

 versy. Whatever theory be adopted Ludwig's facts remain. 

 During the last ten or twelve years, Ludwig's pupils 

 experimented largely on the process of Nutrition as mani- 

 fested in the absorption and fate of proteids, sugars and fats. 

 Numerous are the investigations on the course of the fat 

 on its way to the blood. With what care and exactness did 

 Ludwig operate when exposing the termination of the 

 thoracic duct! Indeed he was an ideal operator, and had 

 he chosen to turn his attention to surgery few would 

 have equalled him in the art. The passage of proteid and 

 sugar into the blood was the subject of many investigations, 

 and so was the effect of the injection of so-called peptones 

 into the blood stream (Schmidt-Mulheim and Fano) where- 

 by the blood of the dog when it was shed was prevented 

 from coagulatino-. Correlated with this are the numerous 

 investigations on the respiratory processes involving a 

 study of the gaseous exchanges in the lungs and the tissues. 



