118 METALLIC STAINS. 



MANFREDI treats fresh tissues as follows (Arch, per le sci. 

 med., v, No. 15) : Gold chloride, 1 per cent., half an hour; 

 oxalic acid, 0'5 per cent. ; they are then warmed in a water- 

 bath to 36, allowed to cool, and examined. Mount in 

 glycerin. Sunny weather is necessary. 



He treats tissues previously hardened in 2 per cent, solu- 

 tion of bichromate of potash, as follows (Hid.). They are 

 put for half an hour into solution of arsenic acid, or into 1 per 

 per cent, acetic acid. They are then put into 1 per cent, gold 

 chloride 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. 



BOCCAEDI (Lavori Istit. Fisiol. Napoli, 1886, i, p. 27 ; Journ. 

 Hoy. Mic. Soc., 1888, p. 155) recommends oxalic acid of O'l 

 per cent, or of 0'25 to O3 per cent, or a mixture of 5 c.c. pure 

 formic acid, 1 c.c. of 1 per cent, oxalic acid, and 25 c.c. of 

 water. Objects should remain in this fluid in the dark not 

 longer than two to four hours. 



KOLOSSOW (Zeit. f. tviss. Mik., v, 1, 1888, p. 52) impregnates 

 for two or three hours in a 1 per cent, solution of gold chloride 

 acidulated with 1 per cent, of HC1, and reduces for two or 

 three days in the dark in a O01 per cent, to 0'02 per cent, 

 solution of chromic acid. 



For the details of the application of the methods of which 

 the principles have been set forth above, and for those of the 

 important processes of impregnation of central nerve organs, 

 the reader is referred to those chapters of Part II which treat 

 of nerve-tissues and organs. 



212. Ulterior Treatment of Impregnated Preparations. Pre- 

 parations may be mounted either in balsam or in acidulated 

 glycerin (1 per cent, formic acid). 



Theoretically, they ought to be permanent if the reduction 

 of the metal has been completely effected. 



In practice, all are doomed to destruction in course of time 

 by after-blackening, and few will be found to survive more 

 than a few months. Ranvier states that this can be avoided 

 by putting the preparations for a few days into alcohol, which 

 possesses the property of stopping the reduction of the gold. 

 But this must be taken to mean that by this means the period 



