68 



although the sarcoplasm is not so well preserved. The muscle should 

 be moderately distended upon cork, before fixing, the ends secured 

 by small pins. 10% formalin or Zenker's fluid or Mercuric chlorid 

 may also be used, the sarcoplasm being much better fixed in di- 

 chromate, osmic acid or formalin mixtures. Iron hematoxylin is 

 particularly indicated as a stain for muscle ( 94). Mallory's con- 

 nective tissue stain ( 120) is found to give an excellent differentiation 

 (Kingery). 



To differentiate muscle in situ, picrofuchsin may be used, which 

 stains muscle yellow or orange, the surrounding connective tissue 

 red. Mallory's connective tissue stain is also frequently useful. 



To differentiate the intercalated discs of cardiac muscle, fix in 

 mercuro-nitric mixture ( 20) ; imbed in paraffin ; stain sections with 

 haemalum ( 89), diluted, 12 to 24 hours; differentiate with acid 

 alcohol; dehydrate, clear, mount in balsam. 



THE NERVOUS SYSTEM. 



An analytical grouping of the numerous methods used in the 

 study of the finer structure of the Central Nervous System is pre- 

 mature. The most salient point is the prominent part that reduc- 

 tion processes seem to play. The more important methods here pre- 

 sented deal (a) with the finer structure of cell and fiber; demonstra- 

 tion of the tigroid substance and fibrillae ; (b) the differential staining 

 of the myelinic nerve fiber (Weigert and Marchi methods); (c) the 

 morphology of the elements (neurones) as revealed by the chrome- 

 silver impregnation methods (Golgi methods) or the use of intra- 

 vitam (methylene blue) methods. 



191. Isolation of Nerve Cells. Employ formaldehyde disso- 

 ciator for the isolation of the nerve cells of the spinal cord and of 

 the cerebral cortex, proceeding as follows : 



Split the spinal cord along its median plane, separating thus 

 the two halves, and place it in an abundance of the dissociating 

 fluid. The cerebral cortex should be cut into small pieces by sec- 

 tions vertical to the surface. Allow it to remain in the dissociator 

 from 2 to 24 hours; for the best results a stay in the fluid of more 

 than 24 hours is not so satisfactory; although isolated cells are 

 readily obtained their processes are broken off much nearer the cell 

 body. 



