NER VE- TISSUE. 1 19 



another important purpose. The myelin of the medullary 

 sheath being a semi-fluid substance perhaps serving 

 either to isolate the axis cylinder or protect it from ex- 

 ternal violence it would inevitably tend to gravitate to 

 the lower parts of the nerves, were it not that it is held 

 in position by being enclosed, so to say, in cylindrical cases 

 /. ^., the neurilemma-cells, between the constrictions. 



The non-medullated nerve-fibres may be demonstrated in 

 connection with the sympathetic ganglion-cells; seebelow. 



i. Nerve-cells : a. Spinal Cord. Small bits of the gray 

 matter from the spinal cord of man, or from the ox or 

 sheep, should be put for ten days in a dilute solution of 

 chromic acid (one to five hundred), and then carefully 

 shaken in a test-tube with water colored lightly with car- 

 mine ; when the bits have become thoroughly broken up 

 into small particles, the tube is allowed to stand for a day 

 or two, until the particles which have settled to the bot- 

 tom are sufficiently stained. The supernatant fluid is 

 then decanted, and with a glass tube a small drop of the 

 disintegrated tissue is conveyed to a drop of glycerin on 

 a slide and covered, pressure on the cells being avoided 

 in the usual way. If the first preparation does not con- 

 tain the required cells, others should be made. In this 

 way, if the shaking be carefully done, the ganglion-cells 

 are freed to a considerable degree from the surrounding 

 parts, and such may be found as present numerous long 

 branching processes, as well as the axis-cylinder process, 

 In addition to the cells, such specimens present frag- 

 ments of connective tissue, bits of naked axis cylinders, 

 and medullated nerve-fibres, myelin-droplets, etc.* 



* Neuroglia or "spider cells " may also be seen. See page 215 



