878 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Objects coloured in this fluid should not be washed in water, but 

 in alcohol of a grade corresponding to that of the solution. 



For diluting alcoholic solutions of carmine, alcohol of the same 

 strength must always be used. 



6. Aniline Dyes. — As a rule, aniline colours and the many others 

 obtained recently from tar by chemical processes, cannot be used for 

 staining objects in toto, and are therefore not much employed in the 

 Zoological Station. In very small objects and sections already cut, 

 very excellent results can be obtained by the methods developed by 

 Bbttcher,* Hermann,"j" Flemming \ 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. 1 1 The solution should be used undiluted, and requires to be 

 filtered from time to time. It colours very quickly objects hardened 

 in alcohol or chromic acid. 



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

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



Dr. Pfitzner,^ from whom the above formula is taken, recommends 

 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. 



Unless therefore it is desired to differentiate membranes or 

 display the various stages of ossification this group may be dispensed 

 with. 



III. Injecting. — Professor Emery, who has lately studied the 

 methods of injection, recommends the following : — 



a. For injection of thick carmine he follows the prescription of 

 Ranvier, in his ' Traite d'histologie technique,' but neutralizes the 

 mass in a more simple way. Acetic acid is added by drops until the 



* Bottcher, Mull. Archiv, 1869, p. 373. Virchow's Archiv, xl. p. 302. 



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

 Tagblatt, p. 105. 



X Flemming, Arch. f. Mikr. Anat, xiii. p. 702; xvi. p. 302; xviii. p. 151; 

 xix. pp. 317, 742; xx. p. 1. 



§ Arch. f. Mikr. Anat., xv. (1878) p. 258. 



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



1 Morph. Jahrb., vi. pp. 478-80, and vii. p. 291. 



