22 



mordant of 4"? iron aluii for two hours. The excess mordant was 

 then rinsed away with distilled water. Staining with 0.5^ 

 aqueous haematoxylin required at least four hours for entirely 

 satisfactory definition. Clean tap-water was used for washing 

 out the uncoDibined stain, sirjce this appears to fix the lake 

 more firmly. The stain was differentiated with a 2% solution 

 of iron alurr, frequently renewed. This process was observed 

 with the rcicroscope, and when the desired effect had been ob- 

 tained, the sections were transferred to tap-water. Thorough 

 washing at this stage is necessary to prevent fading of the 

 stain, and the slight alkalinity of ordinary tap-water appears 

 to be a factor aiding in its preservation. 



4. The ChloT-iie of Vanaiiurr Kethod. 



The technique required for staining with the chloride of 

 vanadiuir, method of Wolters ( '90) is somewhat troublesome, but 

 the results, when obtained, certainly justify the means. Nerve- 

 cells, axis-cylinders, ependyma, and neuroglia are all defined 

 in one and the same section, Mo other method known to me gives 

 so comprehensive a picture for general study. Its sole value 

 lies, however, in the purely general scope of the results. 



It is hardly necessary to give a description of the process 

 here, since its essentials are outlined in Lee (19C0, p. 410). 



