268 A MANUAL OF VETERINARY PHYSIOLOGY 



grammes (20 gallons) in twenty-four hours. This, of course, is 

 no guide to the amount of lymph in the body, as the thoracic 

 duct is a mixture of body lymph and chyle from the intestines. 

 In the observation mentioned on the cow the amount of material 

 collected from the duct was more than double the blood in the 

 body ; and if, as is usual, we regard two-thirds of the contents 

 of the thoracic duct flow to represent chyle and one-third lymph, 

 it still leaves the lymph flow at a very high figure — in fact, nearly 

 equalling the entire blood-content of the body. As a matter of 

 fact, the total lymph in the body is unknown ; it has been sup- 

 posed that it may be two, or even three, times greater than that 

 of the blood. 



In the following table from Colin the amount of mixed chyle 

 and lymph flowing from the thoracic duct was measured ; the 

 minimum represents a period of comparative digestive quies- 

 cence ; the maximum amounts represent digestive activity. 



Horse - 14 to 40 kilogrammes (24 to 70 pints) in 24 hours. 



Ox - 20 to 91 ,, (35 to 160 pints) in 24 hours. 



Sheep - 3 to 9-5 „ (5 to 16 pints) in 24 hours. 



Dog - i- 3 to 2* 6 ,, {2.\ to 4! pints) in 24 hours. 



Formation of Lymph. — The method by which lymph is formed 

 has been the subject of great difference of opinion and innumer- 

 able experiments. The question is still unsettled, so that it is 

 necessary to present both views of the case. The difficulty in 

 explaining the production of lymph lies in the fact that the 

 blood system and lymph system of vessels do not communicate ; 

 both, in fact, are closed systems, while between them lies the 

 tissue spaces. What has to be explained is the passage of fluid 

 from one to the other across this space. If secretory nerves had 

 a definite existence in lymph production, all difficulties would 

 disappear ; but though these have been suspected, and by some 

 even described as existing, the balance of evidence is against their 

 presence. But even quite apart from the existence of a special 

 nervous mechanism, there are other grounds on which the theory 

 of lymph formation could easily.be explained — viz., on a physical 

 basis, as of filtration, or diffusion ; but, unfortunately, these 

 frequently fail, under experimental inquiry, to behave in the living 

 body as they do in the dead cell, though, in spite of this, physical 

 processes have been, and continue to be, invoked as an explanation 

 in those cases where their action is not negatived by experimental 

 methods. Finally, the explanation of the selective action of the 

 living tissue-cells has been urged as the real explanation of the 

 phenomenon. As a matter of fact, it is no explanation, though 

 it may, and probably does, tell us something of what is occurring, 

 or fixes on the means by which it is taking place. Nevertheless, 



