226 PRACTICAL NOTES ON HISTOLOGY. 



logwood, and examine. Or inject quarter per cent, gold solution 

 from the aorta or carotid of a young rabbit, until the eyeball is 

 tense ; after half-an-hour cut it out and place for a day in acidu- 

 lated water, then excise the cornea, and examine in glycerine. 



General Method.— Place the whole eye in Miiller's fluid for 

 three to four weeks, cut with a sharp knife into anterior and pos- 

 terior halves, wash well in water to remove the yellow colour. The 

 decoloration is hastened by placing them for several minutes in 

 a one per cent, solution of chloral, then for a day in alcohol, 

 then to absolute alcohol for twenty four hours. Then place for 

 twenty-four hours in celloidin dissolved in equal parts of 

 sulpholine, ether, and absolute alcohol ; lay in a paper box, fill up 

 with the celloidin solution, and when this has become changed 

 into a gelatinous, elastic mass, put into alcohol (seventy to eighty 

 per cent.), in which it becomes hard and can be preserved 

 indefinitely. Cut beneath alcohol or flood the knife, stain in 

 logwood, wash well in water, clarify in oil of bergamot, and 

 mount in balsam. 



Preparing Eyes of Gasteropods.— Use a concentrated solution 

 of perchloride of mercury, which keeps the rods in a good condi- 

 tion for hardening in Miiller's fluid ; picric acid or alcohol may 

 be used. It is best to stain in logwood ; first oz'erstSLin, decolor- 

 ise with a weak solution of alum for a period of several hours to 

 some days. Nuclei and cell show well. Cut in paraffin. Foi 

 macerating use a two or three per cent, solution of chromate of 

 potash, or it may be concentrated and diluted with a weak oxalic 

 acid solution, or Miiller's fluid. Fresh material can be examined in a 

 few days, but hardening takes a few weeks. It is advised to dissociate 

 the macerated and stained specimens when in section, and to 

 separate its elements by tapping on a cover glass. 



The Entire Eye.— Remove directly after death. Open by a 

 short incision through the sclerotic, midway between the cornea 

 and the entrance of the optic nerve, and then place in some 

 hardening fluid, as before stated. Much depends on the care 

 taken in hardening and fixing. In chromic acid solutions, 

 which are very good, there are two important objections to their 

 indiscriminate use as fixing and hardening agents : — (i) They 



