34 FIXING AGENTS. 



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. 



A solution containing 5 g. sublimate, 0'5 g. sodium chloride, and 100 c.c. 

 water, has been quoted as " solution of GAULE." 



49. Cyanide of Mercury (KEISEB, BibliotU. Zool, H. vii, 1 Halfte, 

 1891 ; Zeit.f. wiss. Mik., viii, 3, 1891, p. 363). Saturated aqueous solution. 

 Keiser found that this solution, warmed to 45 to 50 C., and allowed to act 

 for from 15 to 60 minutes, and then washed out with 70 per cent, alcohol, 

 was the best of all fixing media for Acanthoccphali. 



50. Chloride of Platinum (Platinic Chloride, PtClJ. An 

 extremely valuable reagent, originally introduced for the study 

 of karyokinesis, but of general application. RABL, to whom 

 we owe the introduction 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 haematoxylin, 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 chro- 

 moformic 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. 



51. Platino-Aceto-Osmic Mixture (HEEMANN, Arch. f. mik. 

 Anat., xxxiv, 1889, p. 58). The author obtained excellent 

 results by substitutng 1 per cent, platinic chloride for the 

 chromic acid in Fleinming's strong formula for chromo-aceto- 

 osmic acid ( 36), the other .ingredients either remaining as 



