874 SUMMARY OF CURRENT RESEARCHES RELATING TO 



2. One volume of No. 1 mixed with 6 to 8 volumes of 70 per cent, 

 alcohol. 



3. At time of using pour into No. 2 as many drops of a concen- 

 trated solution of crystallized heematoxylin in absolute alcohol as 

 suffice to give the required depth of colour. A good solution should 

 be violet inclining a little to blue. The red tinge that arises after 

 the fluid has stood for some time, indicates that it has become slightly 

 acid, in which condition it is unfit for use. To restore its proper 

 colour, it is only necessary to open a bottle of ammonia over the 

 mouth of the bottle holding the hematoxylin in such a manner that a 

 very small quantity of the gas will mix with the fluid. If too much 

 ammonia gas be added, a precipitate is produced which spoils the fluid. 



If the colour appears too strong, the fluid may be diluted with 

 solution No. 1. 



Before immersing objects in this fluid, great care should be taken 

 to free them from the least trace of acid by frequently changing the 

 alcohol. If this is not done thoroughly, the acid left in the prepara- 

 tion will sooner or later cause the colour to fade ; and such results 

 have led to the erroneous conclusion that hematoxylin will not give 

 durable preparations. Dr. Mayer has found that the fading is entirely 

 due to the presence of acid, and that with proper precautions the 

 staining is permanent. 



Small objects are best stained in a weak solution, which colours 

 more slowly but with greater clearness than stronger solutions. After 

 staining, Kleinenberg transfers objects to 90 per cent, alcohol. In 

 case of over-staining, the colour may be partly removed by adding a 

 little oxalic acid or hydrochloric acid (^ per cent, or less) to the alcohol 

 containing the objects. The acidulated alcohol is allowed to work 

 until the colour is slightly reddened. On transferring to pure alcohol 

 the colour passes again into a permanent blue-violet. 



2. Mayer's Cochineal Tincture. — This medium is very similar in 

 most respects to hematoxylin, and is made by soaking 1 gramme 

 powdered cochineal in 8-10 ccm. 70 per cent, alcohol for several days, 

 and then filtering. 



The clear deep red fluid thus prepared may, like heematoxylin, be 

 used in all cases where it is desirable to stain with an alcoholic solu- 

 tion, and will be found particularly useful for objects that, by reason 

 of the thickness of the walls or other peculiarities, are not easily pene- 

 trated by the ordinary aqueous solutions of carmine. It is particularly 

 suited for the Arthropoda, whose chitine only allows the dye to 

 penetrate with difficulty. 



It is necessary, before immersing larger objects in this fluid, to 

 leave them a short time in 70 per cent, alcohol, otherwise there may 

 be a precipitate. The time required for staining will vary from a few 

 minutes to even days, according to the nature and size of the object. 

 For small objects, such as very thin sections, minute worms, Protozoa, 

 the lower Arthropoda, &c, an immersion of a quarter of an hour, 

 sometimes even less, is usually sufficient. With larger objects re- 

 quiring considerable time, it is important to use a large quantity of 

 the fluid, otherwise the amount of colouring stuff in solution might 



