410 A MANUAL OF PHYSIOLOGY 



states that if time enough be allowed, the maximum concentra- 

 tion of sodium chloride in the lymph, after intravenous injection, 

 becomes approximately the same as the maximum in the blood, 

 this fact loses its weight as an argument in favour of the filtra- 

 tion hypothesis when we remember that, according to Asher, 

 all the solids of the lymph are markedly increased when even 

 small quantities of crystalloids are injected into the veins. Nor 

 is it at all easier to explain lymph formation as a matter of 

 osmosis or diffusion combined with filtration. Lazarus-Barlow 

 found, for example, that in the great majority of his experiments 

 the injection of a concentrated solution of sodium chloride, 

 dextrose or urea into a vein was followed, not by an initial diminu- 

 tion in the outflow of lymph (as might have been expected if 

 the exchange of water between the blood and the tissue spaces, 

 and between the tissue spaces and the lymph capillaries, was 

 regulated solely by differences in osmotic pressure), but by an 

 immediate increase. And Carlson has shown that the osmotic 

 pressure of lymph coming from the active salivary glands, as 

 measured by the freezing-point method, may, under chloroform 

 or ether anaesthesia, be distinctly less than that of the blood- 

 serum. Water must therefore be passing from a liquid of higher 

 to one of lower osmotic concentration. 



So far we have considered the passage of the lymph con- 

 stituents, on the one hand through the endothelium of the blood 

 capillaries into the tissue spaces ; on the other, from the tissue- 

 spaces through the endothelium of the lymph capillaries. But 

 it is not to be supposed that the liquid lying in clefts, partly 

 bounded by blood capillaries, partly by lymph capillaries, partly 

 by tissue-cells, should be affected solely by the first two. The 

 third anatomical element must contribute something to, or with- 

 draw something from, the tissue liquid, and may thus play a 

 part in the formation of lymph from the latter. The recent 

 researches of Asher and his pupils have raised the question of 

 the relation between the physiological activity of the organs, 

 and especially of the glands, and the formation of the lymph. 

 They conclude that the common doctrine that lymph is simply 

 a diluted blood-plasma is erroneous. Lymph, they say, far from 

 being a mere filtrate or even a secretion from the blood, is formed 

 by the activity of the organs, and may actually be absorbed by 

 the blood from the tissue spaces. In fact, according to their 

 view, the intravenous injection of lymphagogues, both crys- 

 talloid and colloid, only causes an increased flow of lymph in so 

 far as it leads to increased glandular secretion. But this generali- 

 zation has had only a short-lived vogue, and one by one the 

 results which seemed to support it have been disproved. For 

 example, it was stated that secretin causes a flow of lymph from 



