32 BIOLOGICAL PHYSICS 



be, special haemogenetic, purposes ere it be eliminated as 

 altogether or wholly effete. Systemic or haemal lymph is 

 more or less apparent and physiologically current in the 

 earliest stages of embryonic development, even from the 

 unicellular primary stage, and, in fact, represents the fluid 

 medium in which is conveyed the first metabolic or living 

 atom to the nascent and fecundated or vitalised germ 

 organism, as well as the continually increasing stores of 

 nutritive plasma, which the succeeding stages of embryonic 

 development, growth, and repair more and more call for 

 and necessitate, until the arrival of that stage of develop- 

 ment at which appear the earliest systemic nerve elements, 

 when an additional or the neural lymph makes itself 

 manifest. This latter, when fully evolved by successive 

 stages of physiological evolution, becomes recognised 

 throughout the completely developed systemic nervous 

 system as the cerebro-spinal lymph or fluid. 



During that stage of embryonic development when the 

 rudiments of the future systemic nervous system are being 

 evolved and differentiated by and from the sympathetically 

 innervated organism, the outgrowing and infolding central 

 nerve structures emit and finally enclose this lymph or 

 fluid, which becomes responsible for the maintaining of 

 the patency of the central neural canal, around which are 

 developed the manifold nerve structures to be known as 

 the central nervous system, consisting of brain, cord, 

 and nerves. The developmental reason for this becomes 

 strongly apparent when we consider that the textural 

 consistence of the early systemic nerve elements is of the 

 most unresisting character, and that, consequently, the pro- 

 vision of an internal fluid support or "cushion of rest" 

 becomes a constructive or working necessity, and, hence, 

 we find that a column of this fluid becomes enclosed 

 which reaches from one end to the other of the rudi- 

 mentary neural tube and vesicles after differentiation of 

 the neurenteric canal. Besides affording a mechanical 

 support to the growing nerve textures this fluid penetrates 

 every vesicular protuberance, as well as nerve trunk, as 

 they are projected or developed into the neighbouring 

 sympathetically innervated organic structures, continuing 

 that mechanical support and bufferage so necessary even 



