152 ORGAN OF SIGHT. 



another including a portion of the posterior half of the choroid. 

 The circuli arteriosi iridis minor et major, the vessels between 

 these, the S3'stem of capillaries of the ciliary processes, and 

 their relation to the arterise ciliares posticse, the system (ar- 

 terial) of the laminse Buischii, and the tributaries of the vense 

 vorticosae, are severally to be studied. 



The crystalline lens, with its several parts (capsule, epithe- 

 lium lining the inner surface of the anterior portion, and the 

 constituent fibres of the lens itself) should be made the subject 

 of careful observation. The h} r aline capsule, with the above- 

 mentioned epithelium, can be demonstrated in a perfectly fresh 

 preparation, in humor aqueus. The structure of the lens fibres 

 may be made out in preparations from the lens of a fowl, or of 

 some large mammal, macerated in very dilute sulphuric acid 

 (one or two per cent.). The fibres exhibit a striated appear- 

 ance, and, if they are sufficiently separated from each other, 

 it may be seen that each possesses a spherical nucleus. 



In preparations of the same kind from the portion of the 

 lens which corresponds to the margin between the anterior 

 and posterior half of the organ, every stage of transition of 

 the epithelium which lines the anterior part of the capsule, 

 into true lens fibres, can easily be made out ; the elements be- 

 coming progressively more and more elongated, and their nu- 

 clei more and more distant from their bases. The best way 

 to ascertain these facts is by means of sections, which show 

 also that, posteriorly, the lens fibres are in immediate contact 

 with the capsule. Vertical sections display the very regular 

 mosaic due to the cutting across of the long, hexagonal fibres. 

 The}' may be made after the lens has been hardened in solu- 

 tion of chromic acid (one-tenth per cent.), or bichromate of 

 potash (one-half to one per cent.). The hardening may also 

 be effected b}' exposing the lens to the air, and allowing it to 

 become almost dry: sections so obtained must be mounted in 

 glycerin. The structure of the corpus vitreum, consisting as 

 it does of a perfectly hyaline gelatinous matrix, with a few 

 extremely pale, small spheroidal cells imbedded in it, may be 

 investigated in the fresh organ, but better in sections made 

 after the bulb has been hardened in a one-eighth to one-half 

 per cent, solution of chromic acid. The staining of the sec- 

 tions with carmine or aqueous solution of anilin will prove 

 very useful for the demonstration of the cellular elements. 



The retina presents, perhaps, a more difficult task to the 

 histologist than any other organ ; the investigation of even the 

 simplest relations of its constituent elements requiring much 

 time ami patience. The introduction of the perosmic-acid 

 method of preparation, however, has, within the last few years, 

 considerably bridged over our difficulties in this respect. 



