494 NEUROGLIA AND SENSE ORGANS. 



straese 13), 1899 ; GREEF, Anleitung zur Mikr. Untersuch. d. Auges, 



Berlin, Hirschwald, 3rd ed., 1910; and the Art. "Retina" in Encycl. 



mik. Technik., 2nd ed., p. 575. 



SZENT-GYORGI (Zeit. f. wiss. Mikr., xxxi, 1914), uses the following 



fluid :- 



Acetone ....... 125 c.c. 



Glacial acetic . . . . . . 5 ,, 



Formalin . . . . . 40 



Sublimate ...... 4 grins. 



Aq. dest. . . . . . .100 c.c. 



Leave whole small eyes in 100 c.c. of this mixture for two to three 

 days, larger whole eyes six to seven days, after which one adds an 

 additional 50 c.c. of acetone to the fixative and leaves for a further two 

 or 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 CaCl, if necessary. Transfer from the acetone 

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

 celloidin embedding. 



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 of! (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 



