The Microscope. 247 



OsMic ACID. —This can be kept as a one per cent, aqueous solu- 

 tion, and should be carefully protected from the light. For staining 

 it shoiild be diluted with distilled-water to one-tenth to one-fifth 

 per cent, solution. It acts slowly, requiring from six to twenty-four 

 liours. It selects fatty tissue, staining it a delicate black or brown. 

 Sections stained with this acid should be preserved in glycerine. 

 The cme per cent, solution can be used as a hardening medium for 

 nerves and small pieces of tissue. Its penetrative power, however, 

 is not great, therefore, the pieces to be hardened should be small. 



PiCKO- CARMINE. — The formula which has proved most satisfac- 

 tory is that prepared after Friedlgender, as follows: 



1, Carmine, 1.00. 



Water of Ammonia, 1.00. 



Distilled - water, 50.00. 



Rub up the carmine with the ammonia and slowly add the water. 



2. A saturated solution of Picric acid. 



Solution No. 2 is added to No. 1, drop by drop, till the precip- 

 itate, which forms at first, is no longer dissolved by stirring. The 

 amount of picric acid necessary is proportionate to the quantity of 

 ammonia present. The mixture is now filtered, and for every 3 ounces 

 a few drops of carbolic acid are added, to prevent decomposition of 

 the fluid. Any cloudiness which may subsequently ensue is dispelled 

 by a few drops of liquor ammonipe. 



This is an exceedingly valuable stain as it acts quickly — a few 

 minutes only being required — and defines sharply. By it the nuclei 

 are tinged a deep-red, the connective tissues assuming a brighter 

 color, whilst muscular tissue, epithelium, etc., have the bright yellow 

 •of picric acid. If the section is first placed for a few minutes in a 

 •dilute aqueous solution of picric acid, the result will be more 

 brilliant. 



The stains given above, with the exceptions of the picric and 

 osmic acids, are for staining single sections. Specimens can be 

 stained in bulk before cutting, though the procedure cannot be recom- 

 mended, as the results are generally uneven and unsatisfactory. As, 

 liowever, the hardening is accomplished at the same time, it may be 

 used as a rapid method. Alcoholic solutions of picric acid, hsema- 

 toxylon or eosin, prepared rather weak, are fluids which act in the 

 way described. 



Hints. — Before placing in the staining- fluid, all sections should 

 be carefully washed in water to remove all traces of alcohol, as this 

 •chemical may precipitate the stain. 



