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having sought for a long time in vain after means of guess- 
ing at these misfortunes and hindrances, the contribution of 
Henoicque came to my sight, according to which by placing 
the tissue treated with chloride of gold in a vessel filled with 
a concentrated solution of tartaric acid, and by putting the 
whole into hot water, a rapid separation of the gold-salt is 
brought about. Accordingly, I tried this method, and my 
endeavours were crowned with the best result, so that I 
obtained always and in every cornea without difference of 
light, and under all conditions the same preparations equally 
complete and equally pretty. I proceed in the following 
manner :—From a rabbit yet alive or just killed, I cut out 
the cornea with a border zone of the sclera of a few milli- 
meters, and place it, after having removed with care the iris or 
ciliary body which was, in some cases, extracted with it, in a 
watch-glass with a pure half per cent. solution of chloride 
of gold, in such a manner that the convex surface of the 
cornea looks upwards, and the structure rests upon its 
scleral border. After three quarters of an hour or an 
hour, I remove it from the gold solution and transfer it, in 
the same position to a vessel containing distilled water. Here 
I allow it to remain from six to ten hours in the light. After 
this time the colour of the cornea, which was at first yellow 
from the action of the chloride of gold, is replaced by a light 
grey or steel grey. I then place the cornea so coloured in 
a small glass flask with a wide neck, in which is a small 
quantity (five to ten cub. cent.) ofnearly concentrated filtered 
solution of tartaric acid. As soon as the cornea has im- 
bibed this fluid and sunk to the bottom of the vessel ac- 
cordingly, we remark that its colour has become much 
deeper, it has become more or less of a greyish violet. I now 
immerse the flask in a capsule into which has been poured 
as much water at 40° to 50° C., as, at least, corresponds to the 
surface of the tartaric acid solution. After a very short time, 
often in a few minutes, the preparation assumes an intense 
violet-red colour, which continually increases until at last 
the cornea, when the water has quite cooled, appears of a 
dirty dark brown-red colour, and with a shining velvety 
surface. I now lift it out and wash it for two hours or more 
either in common or in distilled water. From eight to twelve 
hours have now been required since the colouring with gold. 
I have prepared a great number of cornea of the rabbit in 
this manner. I cut out the cornea usually between eight 
and nine o’clock in the morning, subject it to the various 
processes enumerated, and between four and five p.m. the 
same is as darkly coloured as possible, and on being washed 
