H1STOLOGICAL METHODS. 233 



This complicated process of nuclear division is known technically as 

 " karyokinesis," and is found throughout the higher animals as well as 

 plants. 



The simple method of fixing and staining, just described, 

 while giving excellent results in many cases, is not always 

 applicable, nor as a rule are the permanent preparations so 

 made satisfactory. For permanent preparations, strong alcohol 

 (for very delicate tissues, absolute alcohol, when procurable, is 

 best) is the most convenient fixing agent, and generally very 

 satisfactory. Specimens may be put directly into the alcohol, 

 and allowed to stay two or three days, or indefinitely if not 

 wanted immediately. When alcohol does not give good results, 

 specimens fixed with chromic or picric acid may generally be 

 used, and there are other fixing agents which will not be described 

 here, as they will hardly be used by any except the professional 

 botanist. Chromic acid is best used in a watery solution (five 

 per cent chromic acid, ninety-five per cent distilled water). 

 For most purposes a one per cent solution is best ; in this the 

 objects remain from three or four to twenty-four hours, de- 

 pending on size, but are not injured by remaining longer. 

 Picric acid is used as a saturated solution in distilled water, 

 and the specimen may remain for about the same length of 

 time as in the chromic acid. After the specimen is properly 

 fixed it must be thoroughly washed in several waters, allowing 

 it to remain in the last for twenty-four hours or more until all 

 trace of the acid has been removed, otherwise there is usually 

 difficulty in staining. 



As staining agents many colors are used. The most useful 

 are hsematoxylin, carmine, and various aniline colors, among 

 which may be mentioned, besides gentian violet, safranine, 

 Bismarck brown, methyl violet. Hsematoxylin and carmine 

 are prepared in various ways, but are best purchased ready for 

 use, all dealers in microscopic supplies having them in stock. 

 The aniline colors may be used either dissolved in alcohol or 

 water, and with all, the best stain, especially of the nucleus, 



