1 882.] in the Zoological Station in Naples. 779 



ones, so that a uniform precision of color would be impossible. 

 In this respect, 



a. Bismarck-brown forms an exception. The preparation of 

 this dye, introduced by Weigert, 1 is extremely simple: 



A saturated solution is made by dissolving the powder in boil- 

 ing water or weak alcohol, or, according to Mayer, in 70 per cent. 

 alcohol. 2 The solution should be used undiluted, and requires 

 to be filtered from time to time. It colors very quickly objects 

 hardened in alcohol or chromic acid. 



b. Safranin. — 1 part sajramn dissolved in 100 parts of absolute 

 alcohol ; after a few days 200 parts of distilled water is added. 



Dr. Pfitzner, 5 from whom the above formula is taken, recom- 

 mends this solution as one of the best for staining nuclei. It is 

 cheap, easily prepared, acts quickly and stains only the nuclei. It 

 works best with chromic acid preparations, from which the acid 

 has been removed as much as possible. 



7. Fiemmiug's methods of treating Nuclei. — The method em- 

 ployed by Bottcher and Hermann of over staining objects with 

 aniline dyes, and then removing the color to any desired extent 

 by the aid of alcohol, formed the starting point of the methods 

 recently published by Flemming. The following is a summary 

 of the more important conclusions reached by Flemming : 4 



A. For Nuclei in general. — I. Objects hardened in chromic acid 

 (i-io per cent, to % percent). 



2. Carefully washed in distilled water. 



3. Stained directly, or further hardened in weak and then 

 strong alcohol. 



4- Objects transferred to weak alcohol (70 per cent.) and shaken 

 for a few moments ; then placed in absolute alcohol for half a 

 minute or longer — till no visible clouds of color appear. The 

 process of decoloring is now completed and the objects must be 



1 Wiegert. Arch. f. Mik. Anat., Bel. xv, p. 258, 1878. 



'According to Flemming, may also !>c dissolved in dilute acetic acid. 



3 Pfitzner. Morph. Jahrb, vi. pp. 47S-S0 and VII, p. 291. 



