350 THE LYMPH AND ITS MOVEMENTS 



poisoned with atropine, the spinal cord and the chorda tympani are stimulated : 

 the greatly augmented supply of blood to the gland produces not a trace of 

 oedema (Heidenhain). 



The difference in pressure between the blood and lymph, therefore, is at 

 least not the only cause of the formation of lymph. 



After the insufficiency of the filtration hypothesis had been established, 

 there still remained a possibility of explaining the formation of lymph by 

 reference to osmotic processes. In the numerous investigations which have 

 been carried on in the last few years many facts have been observed which 

 present no special difficulty for this hypothesis. But there are other phenom- 

 ena which cannot be explained so simply, and which have led therefore to the 

 hypothesis that not only the difference in pressure and the osmotic processes, 

 but some specific secretory process in the capillary wall also is concerned in 

 the formation of lymph (Heidenhain). 



Of the facts which led Heidenhain to adopt this view, some have lost much 

 of their force, in view of more recent work ; others, however, are not yet satis- 

 factorily explained from the physical point of view. We shall discuss briefly 

 and in order the most important of these phenomena. 



1. If a hypertonic solution of common salt or of sugar be injected into the 

 blood vessels, within a short time a large quantity of water passes from the 

 lymph into the blood, while simultaneously the salt or sugar rapidly disappears 

 from the blood, and the lymph stream becomes greatly augmented for a long time. 



This phenomenon might be explained by saying that the vascular wall is 

 less permeable for sugar (or salt) than for water; consequently water passes 

 into the blood vessels by osmosis until the sugar can pass out. Once out of the 

 vessels the sugar in its turn draws water from the tissues and thus occasions 

 the increase of lymph. Among the difficulties which such an explanation en- 

 counters is this, that, according to Heidenhain, the content of sugar in the 

 lymph surpasses that found at the same time in the whole blood or in the serum : 

 the escape of sugar from the blood, therefore, cannot be explained by any process 

 of osmosis, but may be due to the activity of the capillary wall. 



Cohnstein, in opposition to this view, remarks that it is not fair, because 

 of the slow movement of lymph, to compare the composition of blood and lymph 

 drawn at the same time, but in order to obtain harmonious results one must 

 compare only the maximum concentrations of the two. If this rule be observed, 

 the maximum concentration of serum is generally higher than that of the lymph. 

 But sometimes the opposite relationship obtains, and this Cohnstein thinks may 

 be because the blood test is not made immediately after injection of the fluid. 

 But, again, it might be said that the injected fluid had not had time to mix 

 thoroughly with the blood. Be that as it may, the phenomena now under dis- 

 cussion can undoubtedly be explained on a purely physico-chemical basis, and 

 constitute therefore no conclusive proof for the secretion hypothesis. 



2. Likewise, the fact emphasized by Hamburger that the osmotic tension of 

 the lymph flowing from the lymphatics of the extremities under perfectly normal 

 circumstances is greater than that of the blood from the corresponding arteries, 

 is not a conclusive proof, for it is conceivable that the lymph owes its high ten- 

 sion to the contained products of decomposition from the tissues (Koranyi). 



3. The following facts appear to be of greater weight. There is a large num- 

 ber of noncrystalloid substances, which when injected into the blood produce a 

 considerable increase in the formation of lymph (Heidenhain). To these belong 



