FIXING METHODS. 25 



corrosive sublimate. Small pieces, about 0.5 cm. in diameter, are im- 

 mersed in this fluid for from three to twenty-four hours, are then washed 

 in running water for twenty -four hours, and then transferred into 70% 

 alcohol. After twenty-four hours the tissues are placed in 8o c / c for the 

 same length of time, and then preserved in go f / c alcohol. It often 

 occurs that after changes in temperature crystals of sublimate are formed 

 on the surface or in the interior of the object. For their removal a few 

 drops of a solution of iodin and potassium iodid are added to the alcohol 

 (P. Mayer). It is a matter of indifference whether the jo c / f , 8o ( /c or 

 90% alcohol is thus iodized. In the further treatment of the object, as 

 well as in sectioning, any such crystals of sublimate will not be found to 

 be a hindrance. Indeed, in the case of very delicate objects it is often 

 more advantageous to undertake their removal after sectioning by adding 

 iodin to the absolute alcohol then used. 



Acetic Sublimate Solution. This is an excellent fluid, and at 

 present much used for embryonic tissues and for organs containing only a 

 small quantity of connective tissue. To a saturated aqueous solution of 

 sublimate, 5^ to 10% of glacial acetic acid is added. After remaining 

 two or three hours or more in this solution, the objects are transferred to 

 35% alcohol, after which they are passed through the higher grades of 

 alcohol. 



Picric Acid. Small and medium-sized objects (up to i c.c.) 

 are fixed in twenty-four hours in a saturated aqueous solution of picric 

 acid (about 0.75%), although an immersion lasting for weeks is not 

 detrimental, especially if the objects be of considerable size. The tissues 

 are transferred to 70% or 80% alcohol, in which they remain until the 

 alcohol is not colored by the picric acid. They are then preserved in 

 90% alcohol. 



Instead of a pure solution of picric acid, the picrosulphuric acid 

 of Kleinenberg or the picric=nitric acid of P. Mayer may be used. 

 The first is made thus : i c.c. of concentrated sulphuric acid is added 

 to 100 c.c. of a saturated aqueous picric acid solution. This is allowed 

 to stand for twenty-four hours, then filtered, and diluted with double its 

 volume of distilled water. The picric-nitric acid solution is made by 

 adding 2 c.c. of pure nitric acid to 100 c.c. of a saturated picric acid 

 solution. Filter after standing for twenty-four hours. 



Rabl's Solutions. C. Rabl (94) recommends the following 

 mixtures, especially for embryos : ( i ) Concentrated aqueous solution of 

 corrosive sublimate, i vol. ; concentrated aqueous solution of picric 

 acid, i vol. ; distilled water, 2 vols. (2) i per cent, aqueous solution 

 of platinum chlorid, i vol. ; concentrated aqueous solution of corrosive 

 sublimate, i vol. ; distilled water, 2 vols. In both cases, after being 

 washed twelve hours in water (in the first preferably in alcohol) the 

 specimens are transferred to gradually increased strengths of alcohol. 



Vom Rath's Solutions. O. vom Rath (95) recommends, among 

 others, the following two solutions: (i) Picric=osmic=acetic acid 

 solution. Add to 1000 c.c. of a cold saturated picric acid solution i 

 gm. of osmic acid, and after several hours 4 c.c. of glacial acetic acid. 

 Objects are fixed, according to their size, in four, fourteen, and forty- 

 eight hours, and then transferred to T$ c /c alcohol. (2) Picric=sub= 

 limate=osmic acid solution. A mixture of 100 c.c. of a cold 

 saturated aqueous picric acid solution with 100 c.c. of saturated sublimate 

 solution is made, into which is poured 20 c.c. of a 2 c / ( osmic acid solu- 



