352 THE LYMPH AND ITS MOVEMENTS 



delegation of the selective power is necessary. But to make this supposition 

 valid, it must first be shown that the distribution of the individual substances in 

 the lymph of the different organs is the same, that, for example, iodine occurs in 

 the lymph of all the organs as plentifully as it does in that of the thyroid gland. 

 Only when such proof has been furnished can we regard the assumption of an 

 active participation of the capillary wall in the delivery of these substances as 

 finally refuted. 



5. We can say nothing definite at present concerning the entrance of proteid 

 and fat into the lymph. What we know of filtration elsewhere, in the opinion 

 of the author, speaks very decisively against the assumption often made, that 

 we are here dealing with a simple physical process of this kind. 



To sum up the foregoing discussion we may say, that purely physical forces 

 such as difference of pressure and of osmotic tension are not of themselves 

 sufficient to explain all the phenomena incident to the formation of lymph. 

 At present we are forced to suppose that the living capillary wall participates 

 in the formation by some sort of a secretory process. This does not exclude 

 the purely physical factors, although we cannot as yet distinguish what part 

 should be ascribed to them, and what to the vital activity of the capillary wall. 



If this view be correct, it follows that the capillary wall * can be thrown into 

 action by the most different substances, including such as are present in the 

 normal composition of the blood ; also that the capillaries in the different organs 

 are different in certain respects. In general they offer a certain resistance to 

 the passage of water and other substances, but after death or under certain 

 abnormal conditions e. g., venous stasis, poisoning with chloroform, chloral, and 

 ether (Magnus) this resistance is more or less reduced. Hamburger seems 

 even to assume that the increased outflow of liquid in venous stasis is caused by 

 the stimulating action of lymphagogic substances collected in larger quantity. 

 The following phenomenon observed by Hamburger may be mentioned in this 

 connection. If a horse with his head perfectly quiet moves his legs, the flow 

 of lymph in the cervical lymphatic trunk increases. We probably have to do 

 here with an excitation of the vascular wall induced by some product formed in 

 the working muscles and given off to the blood. 



Against the general view which is given most prominence here it might be 

 objected that the capillary wall is so thin that it is bound to permit a plentiful 

 filtration, and that this physical process must therefore play a much greater 

 part than has here been assumed. It appears, however, that other living animal 

 membranes, if they are uninjured, do not permit any filtration. This is the 

 case, for example, with the lung of the frog, and with the membrane of Descemet 

 (Leber) in the eye. When they have been killed they filter very well ; but in the 

 living state they do not let a single drop of an indifferent liquid pass through. 

 The thinness of the capillary cells signifies nothing against the assumption that 

 they can develop a powerful secretory activity. They are thin because they live 

 immediately in the blood and hence need not maintain a reserve store of material 

 within their own borders. 



4. THE LYMPH GLANDS 



Our information as to the functions of the lymph glands is at present 

 very meager. From what we know of the leucocytes on other grounds it is 



1 And possibly the wall of the lymphatic vessels ; see note page 347. ED. 



