NEUROGLIA, AND SENSE ORGANS. 443 



vapour. According to Eanvier [Traits, p. 954) you raay 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 

 calfj 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 

 opened 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, § 44 ; it is then washed in running water, and 

 suspended 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-Dtjvigneatjd {Arch. Anat. Mier., ix, 1907, p. 317j. 



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 recom- 

 mend. 



Leber (Mimch. med. Wochenschr., xli, 30, 1894; Zeit. wiss. Mile, xii, 

 1895, p. 266) advises a solution of formol 1, water 10. After a few days' 

 hardening in this, the eyes may he cut through, it is said, without de- 



