478 BLOOD AND LYMPH. 



animal was A =0.615 C. Back in the tissues, where phys- 

 iological oxidations are going on, this difference is probably 

 greater, and greater in proportion to the activity of the tissues. 

 We can understand that in this way functional activity of an 

 organ may result in attracting more water from the blood-capil- 

 laries into the tissue spaces and may thus cause an augmented 

 'flow of lymph. It is to be borne in mind that the liquid of the 

 tissues may be drained off not only through the lymph-vessels 

 but also through the blood-vessels. That liquids injected directly 

 into the tissues or special substances dissolved in such liquids may 

 be absorbed directly by the blood has long been known. Magendie, 

 for example, proved that when a poison was injected into an organ 

 which was connected with the rest of the body only by its blood- 

 vessels, the animal quickly showed the symptoms of a correspond- 

 ing intoxication. Ordinary hypodermic injections are absorbed 

 much more quickly into the general circulation than would be 

 the case if they were obliged to traverse the lymph-vessels and 

 enter the blood through the thoracic duct. Meltzer has shown 

 that this absorption by the blood from the tissue spaces takes 

 place with especial promptness if the injection is made into a 

 mass of muscular tissue. 



The liquid in the extravascular tissue spaces is, in fact, sub- 

 ject to a play of influences from several sides, and it is the bal- 

 ance among these competing influences which determines at any 

 time the amount and composition of this tissue lymph. Thus, 

 the supply of this liquid is furnished, on the one hand, by water 

 and dissolved substances coming to 'it from the blood in the 

 capillaries, on the other hand, by water and dissolved substances 

 derived from the great reservoir contained in the tissue cells. 

 The amount of the tissue lymph is continually depleted on the 

 other side by water and dissolved substances passing back into 

 the capillaries, or into the tissue elements, or, finally, into the 

 lymph capillaries. The amount that passes by this latter route 

 varies greatly in the different tissues, and in the same tissue 

 may be influenced greatly by pathological as well as normal 

 changes in conditions. 



Summary of the Factors Controlling the Flow of Lymph. 

 We may adopt, provisionally at least, the so-called mechanical 

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

 activity are, first, the intracapillary pressure tending to filter 

 the plasma through the endothelial 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- 



