INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 941 



it is evident that many experimenters have failed to hit upon a com- 

 bination satisfactory in all points. The chemical nature of the 

 colouring material of logwood is fairly stable, and affords no reason 

 for any uncertainty, and it appeared desirable therefore to determine 

 under what conditions the solution would yield the best results. 



The colouring material consists of two substances— hasmatoxylin 

 and haematein, differing by two equivalents of hydrogen. Hajma- 

 toxylin (containing the larger amount of hydrogen) is soluble in 

 alum solution, while hfematein is slightly, if at all so. The latter is 

 of no use for colouring animal tissues. Haematoxylin forms com- 

 pounds with various metallic oxides which are soluble in alum 

 solution also ; and if a tissue be stained with hsematoxylin, or with 

 haematoxylin and a metallic oxide, and immersed in an aqueous 

 solution of alum, the colour will be all discharged from the tissue 

 and taken up by the solution ; and the solution will thus take up 

 fresh quantities of htematoxylin compound until it roaches a point of 

 saturation beyond which it will take no more from tissues, but will, 

 if over-saturated with it, give up the colouring matter freely to 

 immersed animal material. Such a solution of hfematoxylin, alum, 

 and metallic oxide has a clear purple colour, becoming red on 

 addition of acids. If alkaline earths, alumina, or hydrated earthy 

 phosphates be suspended in it, they will absorb the colour, and the 

 solution becomes purple. If the solution be treated with a very small 

 percentage of a chromate, the purple will gradually be replaced by 

 a yellowish -brown colour ; or if a tissue which has been stained 

 with alum-logwood solution be immersed in an exceedingly dilute 

 bichromate solution, the purple will sooner or later be replaced by 

 the yellow tint. If a section of any abnormal caseous concretion or 

 abnormal growth be immersed in a neutral solution of alum-logwood, 

 it will become of a more bluish purple than ordinary tissue, evidently 

 from the presence in it of more than an ordinary amount of alkaline 

 earthy matter or phosphate. 



When the above facts are taken into consideration, it will appear 

 unreasonable to exi^ect tissues hardened in chromic solutions of any 

 kind to colour as readily with an ordinary logwood solution as they 

 would do if immersed in the fresh state. Sections of chromic- 

 hardened tissues are exceptionally difficult to free from chromic com- 

 pounds most probably because part of the chromic acid is in chemical 

 combination and insoluble, and when freed from the hardening 

 material the tissues will not be left in the natural neutral state, and 

 thus less readily will the nuclei take up the colour. But it has been 

 found that hardened tissues if cut into sections and well washed, may 

 be as readily stained with logwood as fresh tissues if the solution be 

 slightly modified. 



It has been found that the cheapest and most practical logwood 

 solution may be made as follows : — Take logwood extract, 6 parts ; 

 alum, 6 parts; sulphate of copper, 1 part; water, 40 parts. All 

 ingredients must be free from iron. Grind the alum, logwood 

 extract, and sulphate of copper in a mortar, and when powdered add 

 sufficient water to form a thin paste ; leave for one or two days with 

 occasional stirring and tlieu filter. The heematein contained in the 



