264 NEKVOTTS SYSTEM. 



is speedily reproduced after its evacuation. In all probabil- 

 ity, it is secreted by the pia mater. 1 



The general properties and composition of the fluid un- 

 der consideration are, in brief, the following : 2 It is perfectly 

 transparent and colorless, free from viscidity, of a distinctly 

 saline taste, alkaline reaction, and resists putrefaction for 

 a long time. It is not affected by heat or acids. As we 

 should expect from its low specific gravity and purely me- 

 chanical function, it contains a large proportion of water ; 

 981 to 985 parts per thousand. It contains a considerable 

 quantity of chloride of sodium, a trace of chloride of potas- 

 sium, sulphates, carbonates, and alkaline and earthy phos- 

 phates. In addition, it contains traces of urea, glucose, lac- 

 tate of soda, fatty matter, cholesterine, and albumen. 



As a summary of the function of the cephalo-rachidian 

 fluid, it may be stated, in general terms, that it serves to 

 protect the cerebro-spinal axis, chiefly by equalization of the 

 pressure in the varying condition of the blood-vessels, accu- 

 rately filling the space between the centres arid the bony 

 cavities in which they are contained. That the blood-vessels 

 of the cerebro-spinal axis are subject to variations in tension, 

 is readily shown by introducing a canula into the subarach- 

 noid space, when the jet of fluid discharged will be increased 

 with every violent muscular effort. 3 The pressure of the 

 fluid, in this instance, could only be affected through the 

 blood-vessels. 



Physiological Anatomy of the Spinal Cord. 



The spinal cord, with its membranes, the roots of the 

 spinal nerves, and the surrounding liquid, occupies the spinal 

 canal and is continuous with the encephalon. Its length is 

 from fifteen to eighteen inches, and its weight is about an 

 ounce and a half. Its form is cylindrical, slightly flat- 



1 Op. cit, pp. 38, 39. 



2 ROBIN, Le$ons sur las humeurs, Paris, 1867, p. 259. 



3 MAQENDIE, Journal de physiologic, Paris, 1827, tome vii., p. 9. 



