74 



BIOLOGICAL PHYSICS 



belonging to the cerebro-spinal fluid, we must not forget 

 that we shall justly attribute to it besides a most 

 important excretory function, in that it bathes and washes 

 the individual nerve units, or neurons, as well as the 

 collective nervous system, collecting the worn and escaped, 

 or disintegrating, material, and floating it out through the 

 numerous exits provided. 



FIG. 9. 



FIG. 10. 

 B. 



f ) 



FIG. 9. VARICOSE MEDULLATED FIBRES FROM THE ROOT OF A SPINAL 

 NERVE. (From Valentin.) 



FIG. 10. B, DIAGRAM TO SHOW THE PARTS OF A MEDULLATED FIBRE. 



i, i, outer ot: primitive sheath enclosing the doubly contoured -white substance or 

 medullary sheath ; 2, a part where the white substance is interrupted, the outer 

 sheath remaining ; 3, axis cylinder projecting beyond the broken end of the 

 tube ; 4, part of the contents of the tube escaped. 



In the performance of these excretory functions within 

 the economy of the nervous system, we think we perceive 

 at work a double, or composite, set of organisms, viz. a 

 pituitary set for the removal of the more solid, and 

 a serous set for the removal of the more fluid materials, 

 finding an entrance into the cerebro-spinal lymph spaces. 

 To the first of these belong the olfactory, besides the 

 pituitary body, and it may be the coccygeal body ; and to 

 the second the pineal body, and the various sweat glands 



