410 
PROF. B. T. LOWNE ON THE 
or in absolute alcohol, and imbedded in paraffin without the use 
of ether or turpentine. Very thin sections are then cut and 
fixed on the slide with shellac and kreosote. The cement must 
be thoroughly dried in the oven at the melting-point of the 
paraffin used, and on no account at a higher temperature. 
The paraffin is next removed by turpentine. The slide is then 
wdped on its bach and edges, and flooded with pure spirit, which 
is drained oft, and immediately afterwards flooded with 75 per 
cent, alcohol and rapidly drained ; Erhlich’s logwood solution is 
then poured on the slide and washed off after a few minutes or 
longer by agitating the slide for a few moments in water, and it 
is again flooded with 75 per cent, alcohol. The washing is the 
most dangerous process, as if the specimens are kept too long in 
water the outer ends of the retinal rods will be entirely dissolved. 
Instead of Erhlich’s logwood a solution of vesuvin in water may 
be used ; it stains the retinal-end organs better than any of the 
aniline dyes. Saffranine in 50 per cent, alcohol, or a solution of 
fuchsine or eosine, may be used for staining, and the washings done 
with spirit, the results of which are often satisfactory. Spider’s 
purple gives excellent results, but the specimens are not permanent. 
The specimen, after flooding with 75 per cent, alcohol, is treated 
with pure alcohol, rapidly drained and cleared with clove- oil 
and mounted in balsam. 
Or, after the first washing in water, the specimen may be 
mounted in glycerine, gradually adding stronger and stronger 
glycerine and water, and draining after each addition. I have 
found that with aniline dyes a very dilute solution of sodium 
carbonate, '5 per cent., or aniline water is not inadmissible for 
washing out the excess of the stain. 
Glycerine mounts, when successful, show the outer ends of the 
rods, either vacuolated or frequently partially dissolved, more 
plainly than balsam mounts. 
The balsam mounts need very careful illumination, otherwise 
it is impossible to see the outer ends of the rods. 
If we trace the optic nerve, we observe that its fibres rim in 
larger or smaller bundles, invested in a very transparent sheath, 
or perineurium. They terminate in the palisade layer by entering 
the fusiform elements. The sheath is continued over the fusiform 
elements, and terminates on the inner surface of the basilar mem- 
brane. The tracheal vessels accompany the bundles of optic 
nerve-fibres, outside their sheath, and continue between the pali- 
