100 COCHINEAL AND OTHER ORGANIC STAINS. 



Mayer points out that by the reaction of alum and calcium 

 chloride there is formed a precipitate of sulphate of lime, and 

 that it will therefore probably be found better to employ 

 chloride of aluminium in the place of alum. 



A powerful, nuclear stain. The stain is permanent, pro- 

 vided (Mayer) that the tissues have been perfectly freed from acid 

 before staining. The solution itself is not permanent. A suc- 

 cessfully prepared fresh solution should be of a violet colour 

 with a decided touch of blue, and should not be at all reddish. 

 If it becomes reddish after standing for some time that is 

 generally because it has become somewhat acid, and the fault 

 may be corrected by holding over the mouth of the bottle 

 containing the solution the stopper of an ammonia bottle ; 

 then on shaking up with the solution the small quantity of 

 vapour of ammonia given off from the stopper, the proper 

 colour is generally regained. 



Small objects are best stained slowly with a very dilute 

 solution. If it be required to dilute a solution already pre- 

 pared for staining this should not be done with alcohol, which 

 may easily cause precipitates to form on the tissues, but with 

 the above-described solution of alum in calcium chloride solu- 

 tion. Over-stains should be washed out with acidulated 

 alcohol. Either oxalic or ( \ per cent.) hydrochloric acid may 

 be used, and the specimens allowed to remain in them until 

 they begin to acquire a reddish hue. The acid is then re- 

 moved by pure alcohol, which restores the pure blue of the 

 stain. 



For large or impermeable objects immersion for days in a 

 very strong solution may be necessary for staining. Osmium 

 and chromic acid objects stain sufficiently. 



185. Dippel's Haematoxylin (DIPPEL, Das Hikroskop, 1882, p. 

 719; Zeit.f. wiss. Mik., i, 1883, p. 95). In accordance with 

 the recommendation quoted in the last paragraph, Dippel 

 makes a saturated solution of chloride of aluminium in alcohol, 

 dilutes it with six to eight volumes of 70 per cent, alcohol 

 and adds the necessary quantity of alcoholic solution of 

 hsematoxylin. 



186. Acid Alcoholic Heematoxylin (Anonymous, St. Louis Med. and 

 8urg. Journ., 1888, p. 165 ; Journ. Roy. Mic. Soc., 1888, p. 517). One part 

 of saturated solution of calcium chloride in proof spirit udded to ei^ r ht parts 



