CIRCULATION IN ITS NERVINE BEARINGS 91 



run, or trickle, and out of which it can gravitate spon- 

 taneously, or be liberated, by ordered function and 

 mechanism, in non-autotoxic manner and safe degree. 



We grant that the cerebro-spinal cavity is occasionally a 

 "shut sac" but the occasion is only when the quantity of 

 fluid within it coincides with its available space, or when a 

 pathological condition arises in which the natural outlets 



FIG. 23. SMALL BRANCH OF A MUSCULAR NERVE OF THE FROG, NEAR 



ITS TERMINATION, SHOWING DIVISIONS OF THE FIBRES. Magnified 



350 diameters. (Kolliker.) 



a, into two ; &, into three. 



are closed. From this it will be perceived that circulation 

 here is essentially necessary to meet nature's wants in the 

 performance of healthy function and the obviation of 

 disease. 



To make plain the nature of this circulation, we shall 

 first consider in some detail the nature of the mechanisms 

 by which it is accomplished, and, in doing so, it may be well 

 to refer shortly to the condition and relations of some of 

 the parts concerned in its embryonic state. 



