2 88 PROD UCTION AND ABSORPTION OF L YMPH. 



blood pressure, carried out by the aid of the mercurial manometer of 

 Ludwig, these authors concluded that the chief factor in the forma- 

 tion of lymph was the pressure of the blood in the capillaries, and 

 that in fact the lymph was essentially only the fluid part of blood 

 which had filtered through the vessel wall into the surrounding 

 tissues. On arriving in the tissues, this lymph or blood filtrate was 

 still under a certain pressure, derived from the blood pressure, and 

 it was this pressure which occasioned the movement of the lymph 

 into and along the lymphatics. Ludwig concluded that the flow and 

 composition of the lymph must be explained not only by filtration 

 of the fluid parts of the blood, but also by processes of osmosis taking 

 place between the tissue juices and the blood. He summarises his theory 

 in the following words : " The blood whjph is contained in the vessels must 

 always tend to equalise its pressure and its chemical constitution with 

 those of the extravascular fluids, which are only separated from it by the 

 porous blood-vessel walls. If, for example, the quantity of blood in the 

 vessels has increased, the mean blood pressure is also increased, and at 

 once a portion of the blood is driven out into the tissues by a mere 

 process of filtration. The same result is brought about when the con- 

 stitution of the blood is altered by the absorption of food or by increased 

 excretion by the kidneys, blood, or skin, or when the composition of the 

 tissue fluids is altered in consequence of increased metabolic changes 

 taking place in the tissues. In the latter case, the changes brought 

 about in the lymph are effected by processes of diffusion." Since it is a 

 condition of the maintenance of life that these chemical changes in the 

 tissues should go on, and that the waste products should be continually 

 excreted by the kidneys, lungs, and skin, there must be at the same 

 time constant changes in the amount and composition of the lymph 

 produced. 1 



The testing of this, the mechanical theory of lymph formation and 

 the lineal descendant of the theory propounded two hundred years 

 previously by Bartholin, has been the object of all subsequent investiga- 

 tions dealing with this question. Although we cannot claim to have 

 arrived at a final decision on the matter, I shall endeavour to show in 

 the following pages that the two processes filtration and diffusion- 

 described by Ludwig, will probably account for the lymph flow and 

 composition in all the cases which have been sufficiently investigated. 



It was shown many years ago by Magendie and others, that chemical 

 differences between blood and lymph provoked a transference of the 

 substance that was in excess from one side of the vessel wall to the 

 other. Thus, if colouring matters, salts, or sugar be injected into the 

 blood, they are very shortly afterwards found in the lymph in various 

 parts of the body. If, on the other hand, these substances be injected 

 into the tissue spaces or into the pleural or peritoneal cavities, their 

 existence can very soon be detected in the blood, whence they make 

 their way into the urine. Other instances of the extreme rapidity with 

 which osmotic interchanges take place between the blood and lymph 

 will be mentioned later on in dealing with the action of lymphagogues. 

 Since these interchanges take place after the introduction of abnormal 

 as well as normal substances into the body, we must assume the general 

 applicability of the results, and look upon processes of diffusion or 

 osmosis as one of the factors in regulating the composition of the lymph. 



1 "Lelirbuch der Physiologic," 1861, Aufl. 2, Bd. ii. S. 562. 



