166 CHAPTER XII. 



But if the necessary salts be added to the tincture itself, 

 then a solution ought to result containing the necessary 

 elements for affording a strong and selective stain with all 

 classes of objects. This proves to be the case ; whence 

 Mayer's new formula, 231. 



208. General Remarks. What are the carmine stains use- 

 ful for ? Is it for staining fresh tissues ? With the excep- 

 tion 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 anilin stains and by some hasmatem 

 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. For most hasmatem solutions have a 

 disastrous tendency to overstain ; and the tar- colours are 

 with hardly an exception entirely inapplicable to staining in 

 bulk. 



Overstains may in all cases be washed out with weak HC1 

 (e.g. O'l per cent.). HENNEGUY (Journ. de VAnnt. et dc In 

 PliysiuL, xxvii, 1891, p. 400) states that overstains may be 

 completely removed by means of permanganate of potash. 

 (But that removes the stain bodily, rather than differentiates 

 it.) All carmine stains, with the exception of aceto-carmine, 

 are permanent in balsam. None of the acid stains, nor any 

 of Grenadier's fluids, should be used with calcareous 

 structures that it is wished to preserve, unless they be taken 

 in a state of extreme dilution. 



209. Choice of a Carmine Stain. Grenadier's alcoholic borax- 

 carmine may be recommended to the beginner as being the 

 easiest of these stains to work with. Carmalum, or one of 

 the alum-carmines, is also an easy and safe reagent. 



210. Pure Carminic Acid is best obtained at present from 

 GRUBLEU & HOLBORN. The price at present is 3s. per 

 10 grms. 



Dr. MAYER writes me that samples obtained elsewhere are 

 sometimes not all that could be desired, containing a per- 



