ZOOLOGICAL STATION IN NAPLES. 223 



methods developed by Bottcher,* Hermann, f Flemming,J and 

 others ; for here diffuse staining may generally be avoided by first 

 over-staining, and then withdrawing the colour to any desired 

 extent by means of alcohol. But to obtain satisfactory results, 

 the sections must be thin enough to allow uniformity of action 

 both to the colouring and the decolouring agent. It is evident 

 that the process cannot be similarly controlled in larger objects, 

 particularly where a dye is used, which, like most of those under 

 consideration, is quickly extracted by alcohol, for in this case the 

 colour would be removed from the superficial layers more rapidly 

 than from the deeper ones, so that a uniform precision of colour 

 would be impossible. In this respect, 



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

 this dye, introduced by Weigert,§ is extremely simple : — 



A saturated solution is made by dissolving the powder in 

 boiling water or weak alcohol, or, according to Mayer, in 70 per 

 cent, alcohol. II The solution should be used undiluted, and re- 

 quires to be filtered from time to time. It colours very quickly 

 objects hardened in alcohol or chromic acid. 



b. Safranin. — i part safranin dissolved in 100 parts of abso- 

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



Dr. Pfitzner,'^* 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 07ily the nuclei. It 

 works best with chromic acid preparations, from which the acid 

 has been removed as much as possible. 



7. Flemming's methods of treating Nuclei.— The method 

 employed by Bottcher and Hermann of over-stainifig objects with 

 anihne dyes, and then removing the colour to any desired extent 

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



* Bottcher. Mul. Archiv., 1869, p. 373. Virchow's Archiv., Bd. XL., p. 302. 



t Hermann. Communicated to the Naturforscherversamralung in Graz, 1875. 

 Tagblatt, p. 105. 



X Flemming. Archiv. f. Mikr. Anat., Bd, XIIL, p. 702, Bd. XVL, p. 302, 

 Bd. XVIIL, p. 151, Bd, XIX., p. 317 and p. 742, B. XX., p. i. 



§ Weigert. Arch. f. Mik. Anat., Bd. XV., p. 258, 1878. 



II According to Flemming, it may also be dissolved in dilute acetic acid. 



* * Pfitzner. Morph. Jahrb., VL, pp. 478-80 and VIL, p. 291. 



