METALLIC STAINS (IMPREGNATION METHODS). 257 



bichromate of potash, as follows : They are put for ten to 

 twenty minutes into 1 per cent, solution of arsenic acid, then 

 into \ per cent, solution of chloride of gold and potassium 

 for half an hour, washed in water, and reduced in sunlight 

 in 1 per cent, arsenic acid solution, which is changed for 

 fresh as fast as it becomes brown. Mount in glycerin. 

 Sunny weather is necessary. 



358. APATHY'S Method (Zeit. f. iviss. Mik., x, 1893, p. 349 ; 

 Mitth. Zool. Stat. Neapel, xii, 1897, p. 729 ; Zeit.f. u-iss. Mik., 

 xv, 1, 1898, p. 79). The material to be used must have 

 been fixed either in sublimate or in a mixture of equal 

 parts of saturated solution of sublimate in 0'5 per cent, salt 

 solution and ] per cent, osmic acid (this more particularly 

 for Vertebrates). The material should be imbedded as 

 quickly as possible, either in paraffin or in celloidin. The 

 paraffin material will keep in a good state indefinitely, and 

 ,so will the celloidin material provided that the blocks be 

 preserved in a thick solution of glycerin jelly with a piece 

 of thymol in it (the jelly is removed before cutting by 

 warming and washing with warm water). Sections are 

 made when desired and fixed on slides, and after the usual 

 treatment with iodine, etc., are either put into distilled 

 water for from two to six hours, or are rinsed in water, 

 treated for one minute with 1 per cent, formic acid, and 

 again well washed with water. 



They are then put for twenty-four hours, or at least over- 

 night, into the gold-bath, which is preferably 1 per cent, 

 gold chloride (see 347), but may be weaker, down to O'l 

 per cent., after which they are just rinsed with water or 

 superficially dried with blotting-paper. The slides are then 

 set up on end in a sloping position, the sections looking 

 downwards, so that precipitates may not fall on them, in glass 

 tubes filled with 1 per cent, formic acid. The tubes are 

 then exposed to light until the gold is reduced, as directed 

 in 355 (you may set them up near a window, and place a 

 reflector of some sort behind them ; a sheet of white paper 

 will do). After reduction you may counterstain, if desired, 

 and mount in any way. After trial I highly recommend 

 this process. I have found it advantageous to reduce in 

 weak solution of formaldehyde, either with or without 



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