CHAPTER XII. 137 



8oc. Ital. Sci., t. vi, No. 9, 1887 ; Zeit. wiss. Mile., vii, 1, 1890, p. 47) 

 have given modifications of Grenacker's formula which do not appear 

 to me rational. 



MAYER (ibid., xiv, 1897, p. 29) makes a stronger stain by taking 2 

 grins, carmine, 5 grins, alum, and 100 c.c. water, and boiling for an hour. 



Alum- carmine is an excellent stain. It is particularly to be 

 recommended to the beginner, as it is easy to work with ; it is hardly 

 possible to overstain with it. Its chief defect is that it is not very 

 penetrating, and therefore unsuitable for staining objects of consider- 

 able size in bulk. 



217. Acetic Acid Alum-Carmine (HENNEGUY, in Traite des Meth. 

 Techn., LEE et HENNEGUY, 1887, p. 88). Excess of carmine is boiled 

 in saturated solution of potash alum. After cooling add 10 per cent, 

 of glacial acetic acid, and leave to settle for some days, then filter. 



For staining, enough of the solution is added to distilled water 

 to give it a deep rose tint. In order to ensure rapid diffusion it is 

 well to bring the tissues into the stain direct from alcohol. Stain 

 for twenty -four to forty- eight hours, and wash for an hour or two 

 in distilled water. Mount in balsam. You can mount in glycerin, 

 but the preparations do not keep so well. 



The advantage of this carmine is that it has much greater power 

 of penetration than the non-acidified alum-carmine. 



218. Cochineal Alum-Carmine (PARTSCH, Arch. mik. Anat., xiv, 

 1877, p. 180). Powdered cochineal is boiled for some time in a 

 5 per cent, solution of alum, the decoction filtered, and a little 

 salicylic acid added to preserve it from mould. 



Another method of preparation has been given by CZOKOR (ibid., 

 xviii, 1880, p. 413). Mayer finds that Partsch's is the more rational, 

 the proportion of alum in it being exactly right, whilst in Czokor's 

 it is insufficient. Partsch's fluid also keeps better. 



RABL (Zeit. wiss. Mik., xi, 2, 1894, p. 168) takes 25 grms. each of 

 cochineal and alum, 800 c.c. of water, and boils down to 600 c.c. 

 He prefers this because it is not so purely nuclear a stain as the 

 others. 



These solutions give a stain that is practically identical with that 

 of alum-carmine made from carmine, with perhaps even more delicate 

 differentiations. 



RAWITZ (Zeit. wiss. Mik., xxv, 1909, p. 392) takes cochineal 4 grms., 

 nitrate of aluminium (or ammonio- sulphate of cobalt) 4 grms., water 

 100 c.c., and glycerin 100 c.c. Only for sections. 



219. MAYER'S Carmalum (Mitth. Zool. Stat. Neapel, x, 1892, 

 p. 489). Carminic acid, 1 grin. ; alum, 10 grms. : distilled water, 



