1558 Journal of Applied Microscopy 



the spinal cord of a cat or dog, should be hardened for several days in an excess 

 of a solution of formaldehyde : 



Commercial formaldehyde - - - - 10 vols. 

 Water - - 100 vols. 



After the nervous tissue has been well hardened, take pieces of suitable size 

 and character, wash them in water to extract the formaldehyde, dehydrate, and 

 finally imbed them in celloidin in the usual manner. The sections should be cut 

 as thick as '20 to 30//, since a considerable thickness is necessary to define general 

 relations. 



The sections are to be brought from distilled water into the mordant of iron 

 alum: 



Ammonia-ferric alum - . - . 4 grams. 

 Distilled water - . . . IQQ c. c. 



The duration of the mordanting is not of especial consequence, but may be 

 some two to four hours in length. The free mordant must now be rinsed away 

 with distilled water, a moment only. Then bring the sections into the stain : 

 Haematoxylin crystals - - - - 0.5 gram. 

 Distilled water . . . . . lOO.O c. c. 

 Staining will require at least four hours for entirely satisfactory definition. 



The uncombined stain is to be washed away with water. Clean tap-water is 

 best, since this appears to fix the lake more firmly. 



The stain now requires dififerentiation. Dilute some of the iron alum solution 

 used as a mordant with an equal volume of distilled water, and pour this over 

 the sections. The full strength, four per cent., may be used later if necessary. 

 Only a few sections should be decolorized at a time, and these should be moved 

 about in the fluid to secure even results. Observe the process of decolorizing 

 with the microscope from time to time, and when the desired effect has been 

 obtained, transfer the sections to tap-water. Nerve-cells and nerve-fibres should 

 appear blue on a light field. 



Thorough washing of the sections after staining is necessary to prevent 

 subsequent fading. The slight alkalinity of ordinary tap-water appears to be a 

 factor aiding in the preservation of the stain. 



Light counter-staining with orange-G is almost always desirable. After 

 washing, bring the sections for one to two minutes into a nearly saturated aqueous 

 solution of orange-G (Griibler's). Dehydrate rapidly with ninety-five per cent, 

 alcohol, clear, and mount in balsam. 



Iron haematoxylin may also be employed in the study of the minute structure 

 of the nerve-cell. Small pieces of the brain or cord should be fixed with the 

 fluid of Flemming, or with the chrome-oxalic mixture given below (2). Imbed 

 in paraffin, and cut the sections quite thin. For such cytological study, it has 

 been found preferable to omit the counter-staining with orange-G. 



2. The Staining Method of Nissl. 



The staining method of Nissl is invaluable for demonstrating the organiza- 

 tion of the nerve-cell in general, as well as for the comparative study of different 

 types of nerve-cells. The cervical cord of the rabbit is a particularly favorable 



