xiv THE LYMPH 525 



elaboration. Accordingly, chemical differences between the lymph 

 and the blood plasma of the capillaries are constantly arising, and 

 promote a continuous diffusion current from the blood to the 

 lymph. In the above example of the mammary gland it is con- 

 ceivable that its secretory epithelia, by constantly subtracting 

 lime from the lymph, set up a persistent diffusion current, by 

 which fresh lime passes continually from the blood to the lymph 

 by way of the capillary walls. That this diffusion current may 

 be rapid enough to provide for the chemical needs of the several 

 tissues will be readily understood on considering the extra- 

 ordinary rapidity of respiratory gas exchanges, arterial being 

 transformed into venous blood in the time during which the 

 capillaries are traversed. Cohnstein also quotes the researches of 

 v. Brasol (1884) and of Klikowicz (1886), which prove that sugar 

 and salts injected into the blood in concentrated solutions pass in 

 a few moments from the blood to the tissues, and thence drive out 

 into the blood such quantities of fluid as considerably to increase 

 the blood pressure and diminish the relative quantity of haemo- 

 globin from 30-60 per cent. These facts show that simple processes 

 of diffusion in the body can sufficiently account for the rapid 

 transport of considerable quantities of solid matters from the 

 blood to the tissues. Undoubtedly the same may occur in the 

 normal formation of lymph when diffusion is aided by filtration. 



There is no necessity to resort to any mechanism other than 

 that of diffusion and filtration to explain the effects of the 

 lymphagogues of Heidenhain's second category. Since these 

 increase the concentration of the blood, much water passes from 

 the tissues into the blood to re-establish iso-tonicity, or equilibrium 

 of osmotic pressure, which raises the pressure in the capillaries and 

 favours filtration, and therewith the lymph stream, along with 

 which the injected substance passes out of the blood. Heidenhain 

 observed that the lymphagogic action of crystalloids was pro- 

 portional to their power of attracting water, which again, accord- 

 ing to v. Limbeck, is proportional to their diuretic action. 



More controversy arises as to the interpretation of the effects- 

 of lymphagogues of the first category. Since the increase in the 

 lymph current cannot be explained by a rise in intra-capillary 

 pressure, which, on the contrary, falls, Starling holds that these 

 substances, which are toxic to the heart, muscles, and leucocytes, 

 are also toxic to the epithelioid cells of the capillary walls, by 

 chemically altering them and rendering them more permeable, so 

 that the normal pressure is sufficient to cause increased filtration. 

 Cohnstein, on the other hand, maintains that the lymphagogic 

 action of these substances must be interpreted as the effect of 

 diminution of the endosmotic equivalent of the blood, and conse- 

 quent diminution in the quantity of water that passes by diffusion 

 from the lymph spaces into the blood capillaries. We know that 



