APP.] STAINING EMBRYOS. 431 



found to stain more thoroughly in this than in 

 the hsematoxylin solution. 



c. With carmine. 



Beale's carmine or some alcoholic solution is 

 the best. Into this the embryo may be removed 

 directly from 90 p.c. alcohol, left for 24 hours, 

 and then placed again in alcohol until required. 



d. With picro-carmine. 



This reagent is useful as will be seen later 

 for staining mammalian segmenting ova and 

 very young blastoderms ; it is used with the 

 greatest success after hardening in osmic acid. 



There are several methods of making picro- 

 carmine, the following is the simplest, and we 

 have found it answer our purpose fairly well. 



To a solution made up of 1 grm. of car- 

 mine 4 cc. of liquor ammonia and 200 cc. of 

 distilled water add 5 grms. of picric acid ; agitate 

 the mixture for some minutes, and then decant, 

 leaving the excess of acid. 



The decanted fluid must remain for several 

 days, being stirred up from time to time; even- 

 tually evaporated to dryness in a shallow vessel, 

 and to every 2 grms. of the residue add 100 cc. 

 of distilled water. 



e. With alum carmine. 



To make it, boU a strong aqueous solution of 

 ammonia-alum with excess of carmine for 10 to 

 20 minutes, filter, and dilute the filtrate until 

 it contains from 1 to 5 p.c. of alum. Add a 

 few drops of carbolic acid to prevent the growth 

 of fungus. 



