64 Neurological Technique 



completely removed from the tissue surrounding it after fixation 

 in formalin. If it is desired to study the development of 

 meduUation, it is particularly important to avoid any stretching 

 or crushing which might result from complete dissection 

 of the fresh tissue. In case of the spinal cord, for example, 

 simply lay it bare, clip out entire such parts of the 

 vertebral column as contain the regions desired, and place the 

 whole in the formalin for several hours before further dissection. 

 To allow better penetration of the fluid it is best to complete the 

 dissection as soon as possible without injury to the tissue. 



2. Any time after 2—5 days of fixation remove such pieces 

 as are desired and wash out the formalin in distilled water 1-4 

 hours. 



For imbedding in celloidin the pieces may be much larger 

 than it would be well to attempt to imbed in paraffin. The 

 larger the piece, the longer it should remain in the various fluids 

 preparatory to imbedding. The times given in the following 

 directions apply to pieces not thicker than i cm. 



3. To dehydrate and imbed in celloidin. — {a) Transfer from 

 water to about 10 volumes of 50 per cent, alcohol for 30 minutes 

 to I hour, [b) Replace 50 per cent, with 70 per cent, alcohol for 

 I hour. 



{c) Replace 70 per cent, with 95 per cent, alcohol for 2 hours 

 or more. 



(d) Change to 10 or 15 volumes of absolute alcohol for 4-12 

 hours. 



(«■) Change to the same amount of ether-alcohol (IX, D) for 

 4-12 hours. 



(/) Replace ether-alcohol with thin celloidin (IX; C) for 

 12-24 hours. 



(^) Replace thin coUoidin with thick celloidin (IX, F) for 

 24-48 hours. 



4. With a spatula or section lifter, mount the specimen in 

 position for sectioning on a wooden or vulcanized fiber' block 



' Vulcanized fiber blocks are far better for general purposes. It is often desir- 

 able to preserve the block containing the tissue, so that sections may be taken from it 



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