PRACTICAL NOTES ON HISTOLOGY. 221 



in strong acetic acid, and then staining with an acid mixture of 

 carmine and glycerine. 



The Lens and Vitreous Humour.— To obtain isolated fibres of 

 the lens, take the fresh eye of any animal, and cut it across into 

 anterior and posterior halves. Place the anterior part, having 

 removed the remains of the vitreous humour, in one-eighth per 

 cent, solution of bichromate of potash. Then scratch through 

 the posterior capsule, which is readily ruptured and curls away 

 from the lens proper. Shell this out and leave in the fluid, the 

 remainder of the eye being rejected. The lens is allowed to 

 remain in the bichromate for two or three days, turning over once 

 or twice. It will be found that it has a tendency to separate 

 along the radiating lines which mark the planes of junction of the 

 ends of the fibres, and if a piece of these lamellae is taken up 

 with the forceps it will tear in the direction of the fibres from one 

 of the planes of junction ; separate the fibres with needles in a 

 drop of the bichromate solution. In eyes prepared in Miiller the 

 lens will be hardened enough to freeze and cut. Stain in eosin, 

 carmine, or logwood, and mount in glycerine or Canada balsam. 

 Frogs or the codfish show the serrations the best. The anterior 

 epithelium may be shown also by staining the fresh lens in silver 

 nitrate and shaving off a thin layer from the anterior surface, or in 

 a solution of i part of fuming nitric acid in 3 parts water and 

 I part glycerine. Remove after twenty-four hours and allow to 

 remain a day in water. Tease a portion of the lens in glycerine, 

 and mount in Farrant or glycerine. 



Formic Acid (sp. gr., 1,020). — Place the lens in sufficient of 



the acid to cover it, remove portions from its surface by needles 



(say, in half-an-hour), tease in a drop of glycerine, or, better, a 



drop of picric acid, and examine in glycerine. If allowed to stay 



for twenty-four hours in the acid, the fibres will be in a perfect 



condition. A mixture of formic acid (sp. gr., 1,020) and water, 



equal parts, isolates the fibres, but causes them to swell. They 



may also be isolated rapidly with a saturated solution of caustic 



potash, and the lens is then found to be in layers. 



If the lens is placed in a sky-blue solution of sulphate of 



copper for eight or ten days, sections can be made in which the 



Journal of Microscopy and Natural Science. 



New Series. Vol. II. 1889. t 



