59 



deal, it is best to put it on the fine hone for a short time before each 

 day's sectioning. Unless experienced in sharpening section knives, 

 it is well for the first few times to work under the direction of one 

 skilled in the manipulation. There are, however, excellent accounts 

 to be found in works on technique [e. g., 17, 21a]. 



Do not be satisfied with any but a smooth edge, keen enough to 

 cut without "pulling," a hair held in the fingers, a quarter of an 

 inch or more from the fingers. When once a good edge is secured, 

 take pains to preserve it. 



With the yellow hone, use a lather of olive oil soap; the blue- 

 green soap stone is rubbed up with water; with the Arkansas stone 

 apply a good thin oil. 



SPECIAL METHODS. 



THE CELL. 



The technique of the Cell is almost coextensive with that of his- 

 tology as a whole, at least as far as concerns the application of the 

 more exact and delicate methods. It is necessary therefore to give 

 here only the more salient points and accepted methods. 



174. General Methods. Hermann's fluid, Flemming's fluid, 

 Zenker's fluid, Mercuric chlorid, Carney's fluids, and Picro-aceto- 

 formol are standard fixers, although special problems may demand 

 other combinations. Iron Hematoxylin, the Ehrlich-Biondi-Heiden- 

 hain triple mixture, Safranin, Gentian Violet and Orange G. are per- 

 haps the most serviceable stains. Of these iron hematoxylin is 

 particularly and universally useful. The Ehrlich triple stain is 

 valuable in the more analytical work and should follow Mercuric 

 chlorid (or Zenker's fluid, Carnoy's fluid) fixation. Safranin and 

 gentian violet, separately as red or blue stains, or successively fol- 

 lowed by orange G (Flemming's triple stain) only after Hermann's 

 fluid, or Flemming's fluid, or similar mixtures. 



175. Chromatin. While regressive stains of the iron hema- 

 toxylin type give valuable chromatin stains, they are not as a rule 

 analytical or selective. In accordance with the recommendation of 

 Heidenhain it is better to stain progressively with dilute solutions 

 if a pure chromatin (basichromatin) stain is desired. 



