558 NEUROGLIA AND SENSE ORGANS 



three days. Transfer to pure acetone for three or four days, renewing 

 on the last day ; then bring the eyes into a vessel of acetone, with a 

 thick layer of desiccated calcium chloride at its bottom, for three or four 

 days, renewing the CaClj, if necessary. Transfer from the acetone into 

 a mixture of half ether, half absolute alcohol, then proceed as for 

 celloidin imbedding. 



According to Ranvier (Traite, p. 954) you may fix the eye of 

 a triton (without having previously opened the bulb — the sclerotic 

 being very thin) by exposing it for ten minutes to vapour of 

 osmium. Then divide it by an equatorial incision, and put the 

 posterior pole for a few hours into one-third alcohol. 



Somewhat larger eyes, such as those of the sheep and .calf, 

 may be fixed in solutions without being opened. But it is 

 generally the better practice to make an equatorial incision, 

 and free the posterior hemisphere before putting it into the 

 liquid. 



The older practice was to use strong solutions of pure osmic 

 acid alone ; but most of the best recent work has been done 

 with chromic mixtures following the osmium. 



Dr. Lindsay Johnson tells me that he now gets the best results 

 by suspending the globe over the steam of a 1 per cent, osmic 

 acid solution raised to the temperature at which vapour is seen 

 to be given off (but not to boiling point) for five minutes in the 

 case of human adults, or for one to three minutes in the case of 

 human infants, all monkeys and small mammals, as in them the 

 sclerotics are very thin. As soon as the sclerotic is felt to be firm 

 to the touch, it should be ojDened by a small nick with a razor just 

 behind the ciliary body ; or if the eye be that of an adult, the 

 cornea and lens may be removed. The eye is then put for twelve 

 hours into the mixture, § 50 ; it is then washed in running water, 

 and susj^ended in a large volume of 2-5 per cent, bichromate of 

 potash for two days, then passed gradually through successive 

 alcohols, beginning with 20 per cent., and ending with absolute, 

 taking five days from first to last. 



Similarly Rochon-Duvigneaud {Arch. Anat. Micr., ix, 1907, p. 317). 



Other hardening liquids, however, also give good results, 

 provided that the fixation by the osmic acid has been properly 

 performed : amongst them liquid of Flemming, and that of 

 Miiller. Formaldehyde mixtures he does not recommend. 



Leber {Munch, med. Wochenschr., xli, 1894, p. 605 ; Zeit. wiss. Mik., 

 xii, 1895, p. 256) advises a solution of formol 1, water 10. After a few 

 days' hardening in this, the eyes may be cut through, it is said, without 

 derangement of the parts. The retina lies flat, and is at least as well 

 preserved as with solution of Miiller. 



See also Heppel {Arch. f. Ophthalm., xlv, 1898, p. 286 ; Zeit. zviss. 

 Mik., xvi, 1899, p. 79), who finds that formol fixes the lens badly, the 

 retina well, so far at least as the absence of folds from shrinkage is con- 

 cerned ; and Herzog {Arch. mik. Anat., Ix, 1902, p. 517, and Encijcl. 



