36 BIOLOGICAL PHYSICS 



and health of the body generally, with its contained viscera 

 and attached limbs, except the brain and systemic nervous 

 system, whose circulation is absolutely sui generis. 



Passing to this latter, the brain and nervous system 

 proper, we find that another series of circulations originates 

 here, by which the life and integrity of that system are 

 maintained, and the waste products arising from its exer- 

 cise and activity removed. Thus, the substance known 

 as the neuroglia, to which the blood circulation conveys a 

 matrix of neuronal nutritive material fitted for the growth 

 and maintenance of the true nervine textures, as well as 

 for their mechanical support, becomes the scene of the 

 origin and formation of the various neurons composing 

 the systemic nervous system. 



Surrounding and accompanying these neurons in their 

 axonal extensions and distribution are their neurilemmar 

 coverings, which are meningeal continuations, separated 

 from the nerve fibres by inter-neurilemmar lymph spaces 

 continuous with the inter-meningeal spaces, and which 

 establish and carry on circulation of the cerebro-spinal 

 lymph, conterminously with the nerve-fibre economy, thus 

 constituting a circulation which is at once protective, insu- 

 lating, and excretory. This circulation constitutes the 

 peri-neural lymph circulation, which everywhere surrounds 

 and accompanies the nerve cells, fibres, and fibrils of the 

 brain, cord, great nerve trunks, and terminal nerve exten- 

 sions, and which is actively concerned in the production of 

 the cutaneous excretion, or sweat, and the maintenance of 

 a proper supply of intra-cranial and intra-spinal fluid, 

 besides assisting to form such fluids as the olfactory, oph- 

 thalmic, otic, oroglossal, gastric, pericardial, pleural, peri- 

 toneal, and synovial. The residual products, so to speak, 

 of cerebro-spinal and neural nutrition and activity are thus 

 utilised for the upkeep of physiological and anatomical 

 fluids, so far as is consistent with the maintenance of health, 

 but in this they unfortunately also may become factors in 

 the production of pathological processes and substances. 



Osmosis and capillary attraction, together with mechani- 

 cal displacement and gravitation, are mainly concerned in 

 this form of circulation, and the proper balance of its 

 physiological and chemical conditions must consequently 



