and Laboratory Methods. 1559 



object for the former purpose ; while for the latter, material should be chosen 

 from sensory ganglia, from the spinal cord, and from the several regions of the 

 brain. 



For the fixation of the tissues, the writer has found nothing so admirable as 

 the chrome-oxalic mixture of Graf : 



Oxalic acid, S per cent. aq. sol. - - 200 c. c. 



Alcohol, 05 per cent. ----- 150 c. c. 

 Chromic acid, 1 percent, aq. sol. - - 150 c. c. 

 Mix in the order as named. 

 This fluid has been given a thorough trial with nervous tissue from many verte- 

 brates, and it has proven uniformly satisfactory. Quite small pieces of perfectly 

 fresh tissue should be fixed for some six hours. It is preferable to wash out the 

 fixing agent with seventy per cent, alcohol, changed repeatedly. 



Thin sections should be made by the paraffin method. It is quite desirable 

 that the sections be mounted in serial order, so that the organization of any 

 given nerve-cell can be traced completely. Mayer's albumen is the safest thing 

 to use for sticking the sections to the slide, since some of the subsequent steps 

 make strong demands on the tenacity of the medium. If the sections are at all 

 wrinkled, a film of water should be interposed in the usual manner. 



Dissolve the paraffin from the sections with xylol, and carry the slide through 

 descending grades of alcohol to distilled water. The sections are now ready for 

 staining. 



The stain of Nissl has the following composition : 



Methylen-blue (Grlibler's BX) - - 3.75 grams. 

 Olive-oil soap ----- 1.75 " 



Distilled water - - - . 1000.00 c. c. 

 Use any pure soap from one of the southern countries of Europe where olive-oil 

 is employed in soap-making. The soap should be cut into thin shavings ; gentle 

 heat may be employed for hastening its solution. The stain should be filtered 

 just before using. 



Rest the slide to be stained on a watch-glass so that its surface will be level. 

 Heat five c. c. of the Nissl stain in a test-tube until it almost boils. Pour the hot 

 stain over the slide, and allow it to act for five minutes. Have at hand a quantity 

 of bibulous paper. Flood the slide w'ith distilled water for the briefest practi- 

 cable time, just enough to rinse away the free stain. Absorb as much of the 

 water clinging to the slide as possible with the porous paper, and immediately 

 pour on the decolorizer : 



Alcohol, 95 per cent. - - - - - 90 c. c. 

 Aniline oil - - - - - - 10 c. c. 



The process of decolorizing is the only part of this method involving especial 

 difficulty, as it lasts only 20 to 30 seconds and must be stopped at just the right 

 point. Hold the slide between the thumb and finger, and rock it back and forth 

 so as to move the decolorizer over the entire field. This reagent should be 

 applied liberally. Watch the process closely. Just as soon as the sections 

 begin to look nearly colorless and take on a delicate rose tint, stop the decolor- 

 izing by flooding the slide with oil of cajeput. 



