THE INTERNAL MEDIUM. 43 



will be found after a time that some salt has got into c and 

 some sugar into b, although there are no visible pores in the 

 partition. Such an interchange is said to be due to dialysis 

 or osmosis, and if the process were allowed to go on for some 

 hours the same proportions of salt and sugar would be found 

 in the solution on either side of the dividing membrane. 



The Renewal of the Lymph. Osmotic phenomena play 

 a great part in the nutritive processes of the Body. The 

 lymph present in any organ gives up things to the cells there 

 and gets things from them ; and thus, although it may have 

 originally been tolerably like the liquid part of the blood, it 

 soon acquires a different chemical composition. Diffusion 

 or dialysis then commences between the lymph outside and 

 the blood inside the capillaries, and the latter gives up to the 

 lymph new materials in place of those which it has lost and 

 takes from it the waste products it has received from the tis- 

 sues. When this blood, altered by exchanges with the lymph, 

 gets again to the neighborhood of the receptive cells, having 

 lost some food-materials it is poorer in these than the richly 

 supplied lymph around those cells, and takes up a supply by 

 dialysis from it. When it reaches the excretory organs it has 

 previously picked up a quantity of waste matters and loses 

 these by dialysis to the lymph there present, which is special- 

 ly poor in such matters, since the excretory cells constantly 

 deprive it of them. In consequence of the different wants 

 and wastes of variou-s cells, and of the same cells at different 

 times, the lymph must vary considerably in composition in 

 various organs of the Body, and the blood flowing through 

 them will gain or lose different things in different places. 

 But renewing during its circuit in one what it loses in 

 another, its average composition is kept pretty constant, and, 

 through interchange with it, the average composition of the 

 lymph also. 



The Lymphatic Vessels. The blood, on the whole, loses 

 more liquid to the lymph through the capillary walls than it 

 receives back the same way. This depends mainly on the 

 fact that the pressure on the blood inside the vessels is greater 

 than that on the lymph outside, and so a certain amount of 

 nitration of liquid- from within out occurs through the vas- 

 cular wall in addition to the dialysis proper. The excess is 

 collected from the various organs of the Body into a set of 

 lymphatic vessels which carry it directly back into some of 



