INTRODUCTION. ^ 



preferable, the crude extract will not answer), dis- 

 solved in 6 c. c. of strong alcohol. This at first 

 produces a light violet, or sometimes a dirty-red 

 color, but on exposure to the light, in an unstop- 

 pered bottle, the color deepens ; after standing for 

 three or four days exposed to the air and light, the 

 solution is filtered, and 25 c. c. each of glycerin 

 and Hasting's wood naphtha (pyroxylic spirit) are 

 added. The solution is now allowed to stand for a 

 clay or two, and is then filtered again, and this filtra- 

 tion is repeated, after standing, until a dark sedi- 

 ment is no longer formed. The color is now usually 

 very deep, and the solution should be kept in a 

 tightly-stoppered bottle. 



Such a solution is usually to be diluted with water 

 before using, the exact degree of dilution depending 

 upon the rapidity with which we wish the specimen 

 to be stained. As a rule, slow staining with a dilute 

 solution gives the best result, and is less likely to 

 cause shrinkage of the specimen. In staining, bits 

 of tissue are placed in a small dish of the solution, 

 so that they are bathed on all sides by it, and 

 allowed to remain until sufficiently colored. The 

 time required will depend on the strength of the 

 solution, and also, to a considerable degree, upon 

 the character and previous preparation of the tissue. 

 The excess of coloring fluid is to be thoroughly 

 washed out of the specimen by water before further 

 manipulation. 



