48 HARDENING AGENTS. 



says that it penetrates somewhat more rapidly, and hardens somewhat more 

 slowly. It should be employed in somewhat stronger solutions, up to 5 per 

 cent. 



81. Neutral Chromate of Ammonia is preferred by some anatomists. 

 It is used in the same strength as the bichromate. Klein has recommended 

 it for intestine, which it hardens, in 5 per cent, solution, in twenty-four 

 hours. 



82. Sulphate of Copper. This salt is seldom used alone, perhaps 

 because it does not give a sufficiently favorable consistency to the tissues 

 hardened by it. I take from the Lehrbuch of Fol (p. 106) the following 

 formula, which was first published by REMAZ, then modified by GOETTE, and 

 is said to be useful for hardening the ova of Amphibia : 



2 per cent, solution of sulphate of copper . . 50 cc. 



Alcohol of 25 per cent 50 cc. 



Rectified wood vinegar, 35 drops. 



Chlorides and others. 



83. Platinum Chloride (MEKKEI/S Solution). The formula of 

 this admirable reagent has been given above, 42 It is an 

 admirable hardening medium for delicate objects. Merkel 

 states that he allowed from three to four days for the action 

 of the fluid for the retina; for annelids Eisig employs an 

 immersion of three to five hours, and transfers to 70 per cent, 

 alcohol ; for small leeches Whitman finds " one hour sufficient 

 and transfers to 50 per cent, alcohol." 



Whitman recommends, for the hardening of pelagic fish 

 ova, a stronger mixture (due, 1 believe, to Eisig), viz. : 



0'25 per cent, solution of platinum chloride . 1 vol. 



1 per cent, solution of chromic acid . . . 1 



The ova to remain in it one or two days (WHITMAN, Method* 

 in Micro. Anat. p. 153). 



84. Palladium Chloride (F. E. SCHULTZE, Arch.mik. Anat., iii (1807), 

 p. 477). This reagent was recommended by Schultze partly as giving to 

 tissues a better consistency than chromic acid or Miiller's solution, and partly 

 on account of a special faculty for penetrating organs rich in connective tissue, 

 that he attributes to it. It is an impregnation reagent, staining certain ele- 

 ments of tissues in various tones of brown. For the somewhat lengthy 

 details of the manner of employing it, the reader is referred to the paper 

 quoted. 



85. Chloride of Zinc is only employed for brain, see post, part ii 



(GlACOMINl). 



86. Picric Acid is a weak hardening agent, little used. It should be 

 employed in saturated solution. 



