476 



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 hquid 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. In fact, we may assume that as blood flows 

 through the capillaries of any tissue there is a twofold movement of 

 water; a movement of water from the inside of the capillaries to 

 the outside, this flow being due to filtration, that is, to the excess 

 of pressure inside the capillary, and a movement of water from the 

 outside to the inside of the capillaries, this flow being due to absorp- 

 tion caused by the greater osmotic pressure of the blood within the 

 capillaries. An important factor in this absorption is the osmotic 

 pressure exerted by the proteins of the blood, a small but constant 

 factor. Under usual conditions we may assume that the filtration 

 stream exceeds the absorption stream, so that the blood flows away 

 from the tissue slightly more concentrated. The water lost by fil- 

 tration is picked up by the lymphatics and returned to the blood 

 by way of the right and left lymphatic ducts. 



