40 ril.M'TKK l\. 



specimens, and found it adiniraM for thv<> purposes. But preparations 

 in i do to test its value from a cytoloi;-u-;il point of view have given me 

 only second-rate results. It is now little used. 



49. Chromic Acid and Platinum Chloride (^MKKKKI/S 

 lutea de* ATo/sr//tm, Leipzig, 1870, p. 19). l^iial volumes of 

 1'400 solution of chromic acid and 1'400 solution of platinum 

 chloride. Objects should remain in it for several hours or 

 even days. After washing out with alcohol of 50 per eent. 

 to 70 per cent., objects stain excellently. If objects thai 

 have been fixed by osinic acid be put into it for some hours,, 

 blackening is said to be effectually prevented. 



This is an excellent hardening medium For del irate objects. 

 Merkol 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. 



A similar mixture, with the addition of 0'25 to 0*1 per 

 cent, of acetic acid, is recommended by BRASS for Protozoa ; 

 and LAVDOWSKY has used for nuclei a mixture of 10 parts of 

 1 per cent, chromic acid, 5 of 1 per cent, platinum chloride, 

 and 100 of 5 per cent, acetic acid. 



Whitman recommends for the hardening of pelagic fish 

 ova, a stronger mixture (due, I 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,, Methods 

 iu Micro. Anat., p. 153). 



Salts. 



50. Chromates. The chromates are amongst the oldest and 

 best tried of hardening agents. The bichromate ot pota>h 

 < -pecially was at one time universally employed for hardening 

 all sorts of tissues. 



l-'i.i MMiNd (Arrh. mile. Aunf., xviii, 1880, p. 352) pointed 

 out that though it preserves cytoplasm well it causes 

 chromatin to swell, and therefore should not be employed 

 for fh> sln.hj of nuclei. But, duly rorrtrlrd n-lth art-lie add, 

 it atl'ords a eorreet and tine lixation of nuclei; whilst piv- 



