218 MICROSCOPICAL RESEAECH IN THE 



2. One volume of No. i mixed with six to eight volumes of 70 

 per cent, alcohol. 



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

 centrated solution of crystallised hsematoxylin in absolute alcohol 

 as will suffice to give the required depth of colour.* 



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

 solution No. i. 



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 preparation will sooner or later cause the colour to fade; 

 and such results have led to the erroneous conclusion that hsema- 

 toxylin 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, alco- 

 hol. In case of over-staining, the colour may be partly removed 

 by adding a little oxalic acid or hydrochloric acid (J 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 perma- 

 ment blue-violet. 



2. Mayer's Cochineal tincture. — i gramme powdered cochi- 

 neal soaked in 8-10 ccm. 70 per cent, alcohol for several days, 

 then filtered. 



The clear deep red fluid thus prepared may, like haematoxylin, 

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

 solution, and will be found particularly useful for objects that are 

 not easily penetrated by the ordinary aqueous solutions of carmine, 

 such as the Arthropods. 



* 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 hasmatoxylin 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. 



