104 CORRESPONDENCE. 



The Robertson Cyanide Bottle {American Naturalist, 

 XXVI., 1892, p. 352). — Prof. C. Robertson uses a wide-mouthed 

 bottle with cork stopper. Out of the lower side of the cork he 

 cuts a hole, into which is inserted a pill-box filled with cyanide. A 

 dozen pin-holes are made in the bottom of the pill-box through 

 which the fumes can pass into the ■ bottle. The bottle can be 

 easily washed out, and has many advantages, especially for flies, 

 bees, and similar insects. It is to be preferred to the ordinary 

 plaster-of-Paris cyanide bottle. 



CorrcBponbence* 



Picrq-Carmine Stain. — In reply to Mr. B. Ives, I see that 

 Squire, in his ''Methods and Formulae,'' recommends Ammonia 

 Picro-Carmine, prepared as follows: — "Carmine, i grm.; Strong 

 solution of Ammonia, 3 cc. ; Distilled Water, 5 cc. Dissolve the 

 carmine in the ammonia and water with a gentle heat ; then add 

 saturated aqueous solution of Picric Acid, 200 cc. ; heat to boiling 

 and filter. This solution gives good results when used as follows : 

 Take a section which has been rinsed in distilled water and lay it 

 out flat on a glass slide, drain off" the superfluous water, then pour 

 on to the section several drops of the Picro-Carmine Solution, 

 warm the slide over a spirit-lamp to a heat that can be borne by 

 the hand when touched with the glass (if the section be too 

 strongly heated, it will shrivel), keep it about this temperature for 

 five or ten minutes, remove the excess of stain by tilting the glass 

 and wiping it wnth a cloth or filter paper, leaving some of the stain 

 in the section, then place one or two drops of Formic Farrant 

 upon the section, and apply the cover-glass. The staining of the 

 section is much improved after it has been mounted two or three 

 days and exposed to daylight. A section of skin gives the most 

 striking results by this method. Nuclei and the transverse muscu- 

 lar fibres stain red, the remainder yellow." W. H. B. 



Will any microscopist kindly tell me the cause of the clouded 

 appearances which occur in apochromatic objectives? I think it 

 is known as the apochrojjiatic disease. If the objective is sent to 

 the makers, they return it as good as new ; but the question as to 

 the defect and its cause is quietly shelved. T. Ashchurch. 



