104 OAEMINE AND COCHINEAL STAINS. 



of red ochre. It ought to dissolve completely in distilled water ; a 1 per 

 cent, solution is hest for use. 



161. Picro-carmine (Weigerf s formula, Virchow's Archived.. Ixxxiv, pp. 

 275, 315 ; Zool. Jahrb., 1881, p. 40). Two grms. of carmine are soaked 

 for twenty-four hours (in a vessel protected from evaporation) in 4 grms. 

 of ammonia; 200 grms. of concentrated solution of picric acid are then 

 added, and the whole put away for twenty-four hours more. Small quan- 

 tities of acetic acid are then added " until the first slight precipitate appears 

 even after stirring." The whole is again put away for twenty-four hours 

 more, when it will he found that there has formed a precipitate that can 

 only partially be removed by filtration ; ammonia is then added drop by drop 

 at intervals of twenty-four hours, until the solution becomes clear. If the 

 solution stains too yellow, acetic acid is added ; if it overstains red, a little 

 ammonia is again added. All badly staining samples of picro-carmine may 

 be improved in the same way by addition of acetic acid or ammonia. 



162. Other Formulae for Picro-carmine. GAGE, Am. M. Mic. 

 Journ., i, 1880, p. 22 ; Journ. Roy. Mic, Soc., vol. iii, p. 501 (very elaborate, 

 and has not afforded me a soluble carmine). FOL, Lehrb. d. vergl. mile. 

 Anat., p. 195. RTTTHEEFOBD, Pract. Hist., p. 173. PAUL MAYEE, Mitth. 

 Zool. Stat. Neapel, ii, p. 20. BABEE, Mon. Micro. Journ., xii, p. 48. 

 PEEGENS, Carnoy's Biologie cellulaire, p. 92. HOYEE, Biol. Centralb., ii, 

 1882, p. 17. BIZZOZEEO, Zeit.f. wiss. Mik., 1885, p. 539. KLEMENSIEWICS, 

 Sitzb. Akad. Wiss. Wien, Ixxviii, 1878, iii, Juni ; Zeit.f. wiss. Mik., i, 1884, 

 p. 501. CUCCATI, Zeit.f. wiss. Mik., vi, 1, 1889, p. 42. 



For Soda-Picro-carmine see LOWENTHAL, Anat. Anzeig., ii, 1887, No. 1, 

 p. 22 ; Anon.. Journ. Roy. Mic. Soc., 1888, p. 518 ; SQUIEE'S Methods and 

 Formula, &c., 1892, p. 35. 



163. Ammonia-Carmine. In my opinion there is no valid excuse for 

 using ammonia-carmine at all at the present day. The most that can be 

 said of it is that it gives a good general stain of preparations of central ner- 

 vous system that have been hardened in chromic acid or a chromic salt. But 

 for central nervous system the stains described in Part II under the head of 

 " Special Stains " are what is generally wanted. 



If, however, such a stain be used, care should be taken to get rid of the 

 free ammonia as completely as possible. This may be done by boiling until 

 the excess of ammonia has evaporated. (So long as free ammonia is present 

 large bubbles are formed in the fluid, and the latter shows a dark purple 

 colour. When the free ammonia has evaporated small bubbles appear, and 

 the solution takes a brighter red tint.) 



One per cent, each of carmine and ammonia in distilled water is a good pro- 

 portion. 



But a safer mode of preparation is that of EANVIEE, given below. 



Staining is best done slowly, in dilute solutions, as many drops of the 

 stain being added to distilled water as will give a liquid of a pale rose tint. 

 Sections should remain in the liquid for twenty-four hours. In this way 

 chromic objects stain well. For sections of encephalon the hardening ought 

 to have been done in a chromic liquid, and all treatment with alcohol ought 



