ZOOLOGICAL STATION IN NAPLES. 221 



3. Picro-carmine. — A very excellent picro-carmine is prepared 

 by Dr. Mayer in the following manner : — 



To a mixture of powdered carmine (2 g.) with water (25 ccm.), 

 while heating over a water bath, add sufficient ammonia to dis- 

 solve the carmine. The solution may then be left open for a few 

 weeks (Mayer), in order that the ammonia may evaporate ; or the 

 evaporation may be accelerated by heating (Hoyer). So long as 

 any ammonia remains, large bubbles will form while boiling, but 

 as soon as the free ammonia has been expelled, the bubbles will 

 be small and the colour of the fluid begin to be a little lighter. It 

 is then allowed to cool, and filtered. To the filtered solution is 

 added a concentrated aqueous solution of picric acid (about four 

 volumes of the acid to one of the carmine solution).* 



In order to protect this fluid against changes attributed by 

 Hoyer f to Bacteria, Dr. Mayer places a small crystal of thymol in 

 the containing bottle; Professor Hoyer uses chloral-hydi'ate (i per 

 cent, or more) for the same purpose. 



4. Acetic Acid Carmine.J — Pulverised carmine added to a 

 small quantity of boiling acetic acid (45 per cent.) until no more 

 will dissolve ; filtered and diluted to about i per cent, for use. 



Flemming used the concentrated solution. 



5. Grenacher's Carmine Solutions.§ — (i) Alum Carmine. — An 

 aqueous solution of alum (1-5 per cent, or any degree of concen- 

 tration)j boiled with J-i per cent, powdered carmine for 10-20 

 minutes ; allowed to cool, then filtered. 



With the addition of a little carbolic acid the fluid will keep 

 for years. It colours quickly, and nuclei more strongly than other 

 parts. Objects should be washed in water after staining. 



(2) Acid Borax Carmine. — a. An aqueous solution of borax 

 (1-2 per cent.) and carmine (J- J per cent.) heated till the carmine 

 is dissolved. 



* The addition of the acid should cease before a precipitate begins to form. 



t Hoyer. " Beitrage z. histolog. Technik." In Biolog. Centralblatt, B. 11, 

 pp. 17-19. 



X Schneider. Zool. Anzeiger, No. 56, p. 254, 1880. 



§ Grenacher. " Einige Notizen z. Tinctionstechnik." Arch. f. Mik. Anat., 

 Vol. XVI., p. 463, 1879- 



None of these solutions to be used where calcareous parts are to be preserved* 



