40 BIOLOGICAL PHYSICS 



takes its origin in the tiny lymph spaces and lacunae (like 

 the primal springs, trickling streams, and head-waters of 

 the river systems of the globe) inter-penetrating the 

 organic units of the various textures apart from the 

 brain and systemic nervous systems, these having a 

 "lymphatic" system of their own. Originating in these 

 comparatively structureless spaces and inter-spaces, the 

 lymph streams converge and pursue their course through 

 a system of at length highly organised vessels, in whose 

 course is interspersed a series of valves and glands whose 

 offices seem to consist of maintaining the flow of, and 

 turning into the current of the blood, an " innocuous and 

 healthy effluent" stream. 



These, in short, constitute the "circulations" or 

 "systems of circulation" distributed to the head, body,, 

 and limbs, but they do not include the "circulations"' 

 still to be found within the various viscera, or within the 

 brain and systemic nervous system. 



The brain and systemic nervous system are fed with 

 blood from the general blood stream in a manner, to- 

 some extent, we have said, sui generis. Thus, the arteries 

 are said to enter the central nervous system " naked," sur- 

 rounded by lymph-filled peri-vascular spaces, and generally 

 unaccompanied by veins. These peri-vascular spaces are 

 filled with lymph, or fluid, from the cerebro-spinal inter- 

 meningeal spaces and, consequently, by the cerebro-spinal 

 fluid which covers and inter-penetrates the whole cerebro- 

 spinal structures, and which (contrary to our general 

 teaching on the subject) we contend flows along, and 

 between, the neurilemmar sheaths of every nerve which 

 leaves the cranial and spinal cavities to the peripheral 

 terminations of the sensory nerve fibrils on the one hand, 

 and the ultimate terminations of the motor nerve fibrils 

 in the muscles on the other. 



We therefore contend that the cerebro-spinal cavity is 

 not by any means a " shut sac," but, on the contrary, that 

 it is permeated by at least two openings, continuous with 

 the sub-arachnoid and sub-dural spaces, and continuous 

 from their exit from the cerebro-spinal cavity to their 

 ultimate termination. 



In the circulation of the blood in the brain it seems to- 



