ro.M POSITION AND FORMATION OF LYMPH. 481 



Summary of the Factors Controlling the Flow of Lymph. 

 We rriuy adopt,, provisionally at, least, the; so-called mechanical, 

 theory of the origin of lymph. Upon this theory the forces in 

 activity are, first, the intracupillary pressure tending to filter 

 the plasma through the eiidotholial cells composing the walls 

 of the capillaries, and second, that form of molecular energy which 

 gives rise to the phenomena of diffusion and osmotic pressure. 

 By the action of this force, the flow of water from one place to 

 another is influenced in accordance with the difference in concen- 

 tration of the dissolved substances. These two forces acting 

 everywhere control primarily the amount and composition of the 

 lymph; but still another factor must be considered; for when we 

 come to examine the flow of lymph in different parts of the body 

 striking differences are found. It has been shown, for instance, 

 that in the limbs, under normal conditions, the flow is extremely 

 scanty, while from the liver and the intestinal area it is relatively 

 abundant. In fact, the lymph of the thoracic duct may be con- 

 sidered as being derived almost entirely from the latter two 

 regions. Moreover, the lymph from the liver is characterized by 

 a greater percentage of proteins. To account for these differences 

 Starling suggests the plausible explanation of a variation in permea- 

 bility in the capillary walls. This factor is evidently one of great 

 importance, although it is not possible to state the character of the 

 changes supposed to occur. One helpful suggestion that rests 

 upon experimental evidence is that the concentration of bases, 

 especially of the calcium, contained in the substance of the vessel- 

 walls, affects greatly their physical properties and permeability. 

 It is evident that constituents of this kind may vary with the 

 character of the food, or in general with the composition of the 

 blood. The idea that the permeability of the capillaries may vary 

 under different conditions has long been used in pathology to 

 explain the production of that excess of lymph which gives rise 

 to the condition of dropsy or edema. The theories and experi- 

 ments made in connection with this pathological condition have, 

 in fact, a direct bearing upon the theories of lymph formation.* 

 Under normal conditions the lymph is drained off as it is formed, 

 while under pathological conditions it may accumulate in the 

 tissues owing either to an excessive formation of lymph, or to some 

 diminution in the process of absorption, or to some interruption in 

 its circulation. 



The scanty flow of lymph from the limbs has been referred 

 by Magnus f to another possible cause, namely, to the great 



* Consult Mcltzer, "Edema" ("Harrington Lectures"), "American Medi- 

 cine," 8, Nos. 1, 2, 4, and 5, 1904. 

 t Magnus, Loc. cit. 



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