276 THE BLOOD AND THE LYMPH 



the proportion of water the lymph may have much to do with maintaining 

 the blood's composition, but how much cannot be stated. There is 

 certainly a strong tendency for the blood to remain constant, often ap- 

 parently at the expense of the lymph's inconstancy. Its percolation 

 through the tissues and its mixture continually with the rapid circulation 

 tend also to make it a means for maintaining the blood's constancy of 

 composition. This is a matter of no little importance; the actuation of 

 the coordinating nervous system is dependent on it, for example, as 

 well as many other essential processes. 



The ventricles of the cerebro-spinal axis are filled with lymph, but 

 what exactly, except to regulate brain-pressure, is the function of these 

 ventricles is uncertain. It is generally supposed that, in this process, the 

 lymph preserves the requisite pressure perhaps partly by means of varia- 

 tion in its rate of transudation into and out of these cavities. The 

 exact relation of the numerous lymphatics of the brain and cord to these 

 reservoirs of lymph greatly needs working-out. (See also under the blood- 

 supply in the chapter above on the nervous system, page 62; and the 

 next chapter for further facts as to the relations of the lymph.) 



