510 



VETERINARY PHYSIOLOGY 



equivalent into the blood — such as sugar or sodium sulphate 

 — leads to a flow of fluid into the blood by a process of 

 osmosis so that it becomes diluted, and also, to an increased 

 formation and flow of lymph. This increase of water in 

 both blood and lymph can be explained only by its with- 

 drawal from the tissues (fig. 206). 



(3) The amount of lymph formed is not great. 

 In man probably only about 100 c.cm. of lymph pass into 

 the blood per hour. Hardly any of this comes from 

 the muscles, although these hold about 70 per cent. 



of the water in the 

 body ; nearly all comes 

 from the abdominal 

 organs, chiefly from the 

 liver, although these hold 

 only about 7 per cent, 

 of the water of the 

 body. 



LYMPH VESSEL 



VEIN 



CELLS 



TISSUE FLUID 



206. — Diagram to illustrate the 

 formation of lymph and the inter- 

 change between the blood and the 

 issue fluids. 



The main exchange of 

 water is directly between 

 the blood and the tissues 

 through the fluid in the 

 tissue spaces and not by 



Fig. 206. — Diagram to illustrate the the lymphatic vessels. 



Fluid injected into the 

 blood-vessels very rapidly 

 transudes to the tissues, 

 and, when blood is withdrawn from the vessels, the water of 

 the tissues very rapidly passes into the vessels to make up the 

 original volume. It is by way of the blood-vessels that serous 

 etfusions into the pleura, peritoneum and other serous 

 cavities are removed, as is indicated by the fact that 

 methylene blue, injected into the pleural cavity, appears in 

 the urine in about 10 minutes, but is not found in the 

 lymph for from 20 to 120 minutes. Such facts as these 

 rather favour the view that the true lymph is separated from 

 the tissue spaces by a layer of endothelium (fig. 206). 



