410 



PROF. B. T. LOWNE OK 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 aud 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 

 wiped on its back and edges, and flooded with pure spirit, which 

 is drained off, 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. Saflranine 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. Spiller'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. 



Grlycerine 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 run 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- 



