GOLD CHLORIDE. 33 



The Planaria are to be placed on their backs and the mixture is to be 

 poured over them. They die extended. After the lapse of half an hour 

 they are brought into alcohol, first of 70 per cent., then of 90 per cent., then 

 absolute, and in two days' time are sufficiently hardened. 



Second formula (Ibid., 1879, ii, p. 46). Make a concentrated solution of 

 corrosive sublimate in picro-sulphuric acid, to which has been added 5 per 

 cent, of acetic acid. 



47. Platinum Chloride. An extremely valuable reagent for 

 the study of karyokinesis. RABL, to whom we owe the intro- 

 duction of this agent, employs an aqueous solution of 1*300. 

 The objects remain in it for twenty-four hours, and are then 

 washed with water, hardened in alcohol, and sectioned. Stain 

 with Delafield's hsematoxylin, or with safranin. 



The action of platinum chloride is similar to that of gold 

 chloride, with the advantage that there is no blackening of 

 the preparations. Rabl finds it give better results (for the 

 study of karyokinesis) than any other reagent except 

 chromoformic acid (32). It causes a slight shrinkage of the 

 chromatin elements, a condition that renders the granules of 

 Pfitzner and the longitudinal division of the elements very 

 distinctly visible (see Rabl's well-known paper in Morph. 

 Jahrb., Bd. x, 1884, p. 216). 



Platinum chloride is an extremely deliquescent salt, and for 

 this reason had better be procured in solution. Ten per cent, 

 solutions are found in commerce. 



For Merkel's solution (chromo-platinic mixture), see ante, 

 42. 



48. 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. 



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

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

 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. 



3 



