600 EXPERIMENTS DEALING WITH 



one factor concerned in lymph formation might be altered, it is 

 impossible to say that a change in permeability is the explana- 

 tion. Thus, Cohnstein accounted for the action of these sub- 

 stances by alterations not in the capillary wall but in the blood. 

 Changes in coagulability and destruction of leucocytes are known 

 to follow injection. And he showed that the blood serum of 

 dogs after injection transuded more rapidly through dead mem- 

 branes than normal serum. 



View of Hamburger. Independently of Heidenhain, Hamburger 

 came to the same conclusion that lymph formation could not be 

 explained as a physical process, and must therefore be a secretion 

 by the cells of the capillary wall. This secretion was stirred up by 

 substances formed during tissue activity and reaching the capillary 

 wall by way either of the tissue fluid or blood stream. 



He worked at the lymph flow along the main cervical trunk of 

 the horse. He looked upon this lymph as arising solely from the 

 muscles of the neck, and overlooked the fact, as Asher pointed out, 

 that it is also derived from the salivary glands, thyroid, brain, &c. 

 His more important experiments were the following : 



(1) Specimens of normal lymph and serum from the jugular 

 vein taken simultaneously may show very different percentage 

 -compositions, and further, the osmotic pressure of the lymph may 

 be higher than that of the serum. 



Cohnstein' s criticism of conclusions drawn from differences in 

 the percentage composition of simultaneous specimens of lymph 

 and serum have already been referred to. Leathes has confirmed 

 Hamburger's observation that lymph from a lymphatic vessel 

 constantly under all conditions has a higher osmotic pressure than 

 serum. This is no objection to a physical theory of lymph forma- 

 tion, but, as Leathes and Starling have pointed out, only to be 

 expected from the fact that products of cell katabolism must pass 

 into the tissue fluid ; a point which will be dealt with later. 



(2) With the lymph from a horse at rest he compared that 

 obtained when the horse ate, and when, with its neck at rest, it 

 did work with the rest of its body. The "food" and "work*' 

 lymphs were increased in quantity and had the same composition. 

 But the carotid pressure was different in the two experiments ; it 

 rose in the first and fell in the second. He concluded that as 

 " work" lymph could not be caused by filtration, it must be due to 

 a secretion stirred up by products of metabolism from the trunk 



