THE STUDY OF THE NERVOUS SYSTEM. 5 



Weigert preparations are treated with a sharp secondary proto- 

 plasmic stain, such as acid fuchsin, the method gives a much 

 larger number of facts and more reliable pictures. In particular, 

 cell bodies are stained and the origin and endings of neurites are 

 sometimes shown sufficiently well to enable the observer to deter- 

 mine the direction of impulses carried by a given tract. Even 

 when this result is not obtained, the double-stained preparations 

 are preferable to ordinary haematoxylin sections for the study of 

 general topographical relations. As a special method, however, 

 the Weigert procedure if used alone and on adult brains, can be 

 relied upon for little in the way of functional relationships. The 

 method is applicable to the study of the course of peripheral 

 nerves by means of sections, and is especially valuable for the 

 analysis of nerve trunks into their components. In addition to 

 the usual Weigert technique, it may be mentioned that with small 

 animals or small brains excellent Weigert effects may be obtained 

 by simple fixation with vom Rath's picro-aceto-platino-osmic 

 mixture, with or without after-staining with acid fuchsin. 



A third special method which has proved extremely valuable is 

 the intra vitam staining with methylene blue introduced by Ehrlich 

 in 1886. This differs from both the preceding in that it is an 

 actual stain of nerve elements. The preparations are in general 

 comparable to those obtained by the Golgi technique, since the 

 pictures are incomplete pictures of the same character. The 

 method gives in addition the internal structure of the nerve 

 elements and is extremely useful for cytological study. It gives 

 also more extensive and reliable information than does the Golgi 

 method as to the details of fiber endings and the structural relations 

 between nerve elements. The method is especially adapted to 

 the study of the peripheral nervous system and to small isolated 

 portions of the central nervous system. It has not yet been 

 extensively used for the study of centers and fiber tracts. It reaches 

 the height of its efficiency where the tissues stained are suitable 

 for study in the living condition. 



Of the great variety of cytological methods which may be applied 

 to the nervous system two require mention as special nerve methods. 

 The first of these is known as the Nissl method and is a selective 



