PERCHLOHIDE OF IRON. 35 



before, or the osmium being diminished one half. Thus, 

 1 per cent, platinic chloride 15 parts, glacial acetic acid 1 

 part, and 2 per cent, osmic acid either 4 parts or only 2 parts. 

 Hermann found that protoplasmic structures are thus better 

 preserved than with the chromic mixture, which I think is 

 undoubtedly the case. It was noted above ( 30) that a chief 

 objection to the use of chromic acid is that it precipitates 

 certain of the liquid albuminoids of tissues in the form of 

 filaments or networks, which are often of great regularity, 

 and simulate structural elements of the tissues. This pla- 

 tinum chloride does not do. On the whole, I take it that this 

 mixture is probably the finest fixative yet discovered. Unfor- 

 tunately it is also the most expensive. 



The after-treatment and staining should be the same as for 

 objects treated with Flemming's solution. 



The remarks in 36, as to the deterioration of Flemming's 

 solution by evaporation of osmium apply with equal force to 

 Hermann's mixture. 



52. Chlorides of Palladium, of Gold, and of Iron. 



Palladium Chloride. Palladium chloride has been recommended by 

 experienced workers. It is used in solutions of 1'300, 1*600, or 1*800 

 strength, for from one to two minutes. Cattaneo recommends it as being 

 the best of fixatives for Infusoria. Tissues are impregnated and coloured 

 brown by it. For small objects one or two minutes will suffice for fixation. 



This salt is found in commerce in the solid state. To dissolve it, take 10 

 grammes of the salt, one litre of water, and four to six drops of hydrochloric 

 acid. Solution will be effected in twenty-four hours. 



Gold Chloride. When used for fixing (and not for the object of 

 staining by impregnation) gold chloride is generally used in solution of 4 

 per cent, strength, for a few minutes (30 at most). Weaker solutions (th 

 per cent.) or stronger (1 to 2 per cent.) may also be used. Wash out with 

 water. 



Gold chloride is one of the most faithful fixing agents we know of. But 

 it is not fitted for general work on account of the capricious fashion in which 

 it undergoes reduction in the tissues, rendering the impregnated elements- 

 unsusceptible of staining. 



Perchloride of Iron (FoL, Zeit. f. wiss. Zool, Bd. xxxviii, 1883, p. 

 491 ; and Lehrb. d. vergl. mile. Anat., p. 102). Fol recommends 1 vol. of 

 Tinct. Ferri Perchlor. P. B. diluted with 5 to 10 vols. of 70 per cent, 

 alcohol. This gives better results than the weaker (2 per cent.) mixture at 

 first recommended. Aqueous solutions do not give nearly so good results. 



Fix for a short time only and wash with alcohol. The preparations are best 

 stained with pyrogallol (see the chapter on Impregnation Methods). Fol 

 recommends this process chiefly for Infusoria, and other ciliated objects, but 



