CLASSIFICATION OF THE FORMULA. 77 



CHAPTER X. 



CARMINE STAINS. 



130. The Sorts of Carmine, Commercial carmine, prepared 

 as it is by very various processes, is of very variable quality. 

 None but the very best should be used for histological purposes. 

 The finest sorts are known in the trade as Nakaret Carmine. 

 They cost about forty shillings a pound ; inferior sorts costing 

 less than a fourth that sum. But the histologist should pro- 

 cure the very best, even though it cost ten times as much as 

 it does. 



131. The Use of Carmine in Staining. What are carmine 

 stains useful for ? Is it for staining fresh tissues ? With the 

 exception of aceto-carmine, No ! Is it for staining sections ? 

 Again, No ! For in nine cases out of ten, sections are better 

 stained by some of the aniliii stains than they can be in any 

 carmine stain. Is it for staining entire objects ? for staining 

 in the mass ? Yes. For in many, if not in most, cases that 

 can be done more satisfactorily by means of carmine than by 

 means of any other known agent. So that until a coal-tar 

 colour shall have been discovered that can beat alum-carmine 

 and borax-carmine on their own ground, these must still hold 

 their sway. As soon as that shall have been done, and it may 

 be done any day, carmine stains will become as extinct as the 

 Dodo. 



132. Classification of the Formulae. In the treatment of the for- 

 mulae given in the following pages I have been guided by the considerations 

 set out in the last paragraph. The best stains for staining in the mass are 

 fully treated, the old-fashioned solutions proposed for staining sections being 

 thrown into the background. The formula set out below are arranged 

 according to the nature of the menstruum. This gives us two great groups: 

 aqueous carmine solutions and alcoholic carmine solutions. Taking first the 

 group of aqueous solutions, I have arranged the formula? comprised in it 

 according to the reaction of the solutions. First come the alkaline ammo- 



