Method XIX 105 



As a matter of fact, formalin produces a slight swelling of the 

 tissues, not enough, however, to be at all objectionable for pur- 

 poses of dissection. In this respect it partakes somewhat of the 

 nature of formic acid. But, beyond this, the specimen fixed 

 and preserved in formalin so nearly fulfils the conditions 

 desired for dissection as to recommend the iise of formalin 

 above all other reagents now employed for such purposes. 



For the simple preservation of the specimen, solutions of 

 formalin ranging in strength anywhere from i per cent, to 5 

 per cent, are sufficient. But for fixation, especially of large 

 specimens, the solution should be stronger. A 10 per cent, 

 solution has been found to give entirely satisfactory results 

 with whole human brains. The eortex of fresh brains thus pre- 

 pared has been found sufficiently well fixed even for histological 

 purposes, particularly for Golgi preparations. 



The solutions of formalin are usually made by adding the 

 required number of volumes of the 40 per cent, formaldehyde 

 to 100 volumes of distilled water. Thus, the so-called 10 

 per cent, formalin is prepared by adding 10 volumes of the com- 

 mercial 40 per cent, solution to lOO volumes of water. 



PROCEDURE. 



I. Removal. — In removing the brain and spinal cord it will 

 be found that the organ holds its shape better if the dura mater 

 is left on. A part at least of the dura mater should be left in 

 position, that its relations to the organ may be studied in the 

 subsequent dissection. 



It will be found a comparatively easy matter to remove the 

 spinal cord with the dura intact. The simplest procedure will 

 be to lay bare the vertejbral column from the dorsal side, remov- 

 ing the. attached dorsal muscles from about the column, and 

 then, with strong bone forceps, clip the /'^<^2V/^j (radices) of each 

 neural arch just below the superior articular processes, or as close 

 to the intervertebral for amenu as possible. Thus the spinal cord 

 inclosed in the dura will be laid bare. Next, free each spinal 

 nerve from its attachment in the intervertebral foramen and 



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