198 THE AMERICAN MONTHLY [July, 



from 1 to 2 mm. thick, is put to macerate in tlie g alco- 

 hol. In 24 hours remove, by the point of the scalpel, a 

 bit of the gray substance and shake it in a test tube 

 containing 15 cc. of distilled water. Shake violently to 

 separate the elements, and add 1 cc. of picro-carmine. 

 When stained (generally in one hour), add 1 cc. of 1 per 

 cent osmic acid. Leave it for 24 hours, and when the 

 elements have settled to the bottom, pour off the super- 

 natant liquid and replace it by distilled water. Renew 

 many times by decanting. To put a drop of the deposit 

 on a slide is all that is needed to obtain a beautiful pre- 

 paration of the nerve cells magnificently colored. To 

 make permanent preparations, when the cells have been 

 well washed and the liquid poured off, add 5 cc. of dis- 

 tilled water with 1 c. of glycerine slightly colored with 

 picro-carmine. Leave the tube open so as to concentrate 

 the liquid by evaporation, and the next day put a drop 

 of the mixture on a slide. To apply the thin cover with- 

 out washing away all the cells is a delicate operation. 

 To accomplish this, mount in glycerine jelly. Place a 

 bit of the jelly on a warm slide, and, when liquified, add 

 in the centre a small drop of the deposit of nerve cells, 

 mingle together with a needle and cover. 



Nerve Fibres.— To separate the nerve fibres of the cord 

 is a delicate operation, to be done only by Ranvier's 

 method of interstitial injection. Insert the needle of a 

 hypodermic syringe, charged with 1 per cent osmic acid, 

 into the antero-lateral column of a perfectly fresh 

 spinal cord from a dog, and gently inject. Remove a 

 small piece with a razor and dissociate it on a slide with 

 water. Stain in picro-carmine ; mount in glycerine. 



Sections. — Of the many methods, we describe only 

 those of use to the beginner. 



Fixing and hardening. — Take a portion, not longer 

 than one centimetre, from the cervical region, one from 



