ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 311 



our various journals on the subject of dyes for histological work. 

 We advise the histologist to ask himself this question : — Is it my 

 object to make for myself a complete educative histological cabinet, 

 or to investigate the subject of stains, and therefore to experiment 

 with the various stains? The operator should settle this question 

 once for all, and hefore he commences his work," 



Staining with Haematoxylon.* — Dr. C. L. Mitchell describes a 

 new and simple method of preparing a logwood staining fluid, by 

 which a permanent, reliable, and satisfactory preparation can, he 

 claims, be easily made, and which places within the reach of every 

 microscopist, a staining fluid " stable in composition, comparatively 

 easy of preparation, and unequalled in the delicacy and clearness of 

 differentiation of its colouring." 



In staining fluids prepared from extract of logwood, the partially 

 oxydized tannin in the liquid gradually absorbs more oxygen from the 

 air and changes to other complex organic compounds ; the colouring 

 matter is also affected by the decomposition, and gradually becomes 

 converted into other substances, and the liquid finally becomes of a 

 dirty muddy colour, and is half filled with a lumpy sediment. This 

 change will be found to take place in all ordinary logwood staining fluids, 

 whether prepared from the extract or from the drug itself, although 

 from the nature of the case those made from the extract would be most 

 quickly affected. The idea therefore occurred to the author, that if 

 the tannin could be removed, and the lake of logwood isolated in a 

 state of comparative purity, a staining fluid could be prepared which 

 might possibly be both permanent and satisfactory, and the following 

 formula is the result of his investigation : — 



MitchelVs Hematin Staining Fluid. 



^ Finely ground logwood ^ij. 



Sulph. alumin. and potash (potash alum) .. ix. 



Glycerine f . 5 iv. 



Distilled water a sufficient quantity. 



Moisten the ground logwood with sufficient cold water to slightly 

 dampen it, place it in a funnel or percolator, packing it loosely and 

 then percolate sufficient water through the drug until the liquid 

 coming from the percolator is but slightly coloured. Allow the drug 

 to drain thoroughly, and then remove it from the percolator and 

 spread out on a paper or board to dry. Dissolve the alum in eight 

 fluid ounces of water, moisten the dry drug with a sufficient quantity 

 of the fluid and again pack in the percolator, this time rather tightly, 

 and pour on the remainder of the alum solution. As soon as the 

 liquid percolates through and commences to drop from the end of 

 the percolator, close the aperture with a tightly fitting cork and allow 

 the drug to macerate for forty-eight hours. Eemove the cork at the 

 expiration of that time, allow the liquid to drain off", and then pour 

 sufficient water upon the drug to percolate through twelve fluid ounces 



* Proc. Acad. Nat. Sci. Philad., 1883, pp. 297-300. 



