I IO HOW TO WORK 



dried. The important fact, however, is this, that the germinal matter 

 of a tissue may be deeply coloured, although the formed material 

 which must be traversed by the staining fluid in the first instance is 

 not stained at all. This is the case with all germinal matter, and it 

 seems to me a fact of far higher significance than is generally ad- 

 mitted. By the process of investigation described it becomes pos- 

 sible not only to distinguish germinal matter in all cases, but to show 

 definitely the mode of formation of the tissue. And in many 

 instances we can determine which is the oldest and which the 

 youngest portion of the tissue.* 



200. Thiersch's Carmine Fluid. Frey (Das Mikroskop) gives 

 Thiersch's fluids for colouring tissues by carmine. 



Carmine, i part. 

 Caustic ammonia, i part. 

 Distilled water, 3 parts. 

 This solution is to be filtered. 

 Oxalic acid, i part. 

 Distilled water, 22 parts. 



One part of the carmine solution is to be mixed with 8 parts 

 of the oxalic acid solution, and 12 parts of absolute alcohol are to 

 be added. 



If the solution is orange-coloured instead of dark red, more am- 

 monia is required, and the orange becomes red. The orange colour 

 may also be used for staining. If crystals of oxalate of ammonia 

 become formed they must be separated by filtration. 



201. Thiersch's Lilac Colouring Fluid. 



Borax, 4 parts. 

 Distilled water, 56 parts. 

 Dissolve and add, of carmine, i part. 



The red solution is to be mixed with twice its volume of absolute 

 alcohol, and filtered. The precipitate of carmine and borax is re- 

 dissolved in distilled water and is ready for use. It colours more 

 slowly than the red solution. 



202. Aniiin colours. The beautiful reds and blues which have 

 been lately so largely used as dyes, popularly known in this country as 

 Magenta and Solferino, have been much employed by microscopists. 

 The colour is not very soluble in water, but is readily dissolved by 



* In a paper on the ova of the stickleback (Microscopical Journal, Jan. 1867), 

 Dr. Ransom has expressed himself against the plan of investigation 1 have fol- 

 lowed. His objec'ions, however, are not valid, and some of the remarks he 

 has made prove, I think, that he has not succeeded in preparing specimens accord- 

 ing to my method. I have replied to some of my friend's statements in a subsequent 

 number of the journal. 



