PRACTICAL NOTES OX HISTOLOGY. 229 



immersion in alcohol, and may be cleared in one of three oils, 

 viz. : — oil of bergamot, cedar oil, or turpentine. The first is 

 most rapid and efficient ; at times, however, we meet with samples 

 of bergamot in which the celloidin cannot be dissolved. Cedar 

 oil is slow in action ; and turpentine often causes a disagreeable 

 shrinkage. Mount in balsam. 



Infiltration with Paraffin.- -Is useful for preparations of 

 embryo eyes, young animals, and of sections of eyes in those 

 cases where examination of the lens is not required. Its chief 

 merit is simplicity. 



The Turpentine Process.— Harden the eyes ; open and stain 

 as before^ transfer from alcohol to oil of cloves, in which leave 

 until cleared. Soak in pure turpentine for several hours, and 

 finally place from eight to twelve hours in paraffin, melted at a 

 temperature not over 50^ C, 122° F. The paraffin displaces the 

 turpentine, and permeates crevices of the tissue. Embed the infil- 

 trated eye in the paraffin ; sections may be cut and sealed to the slide. 

 The most serviceable cement to use is a mixture of clove oil and 

 collodion. It is practically impossible to stain sections after 

 they have been cut and sealed to the slide. [By this method the 

 lens crumbles to pieces.] 



After Staining.— The eye is put in a mixture of alcohol and 

 ether, equal parts, for twenty-four hours, and then submersed in 

 pure chloroform for two days. It is finally placed in melted 

 paraffin for twelve to forty-eight hours, and is treated subsequently 

 as in the former case. By the use of chloroform the treatment 

 with turpentine and clove oil is avoided. The eye must be 

 stained in bulk. 



Retina.— Miiller's fluid. Open a fresh eye as above, place in 

 fluid for two or three weeks, change as often as its altered appear- 

 ance affords an indication of necessity; transfer, after washing, to 

 strong commercial alcohol. It takes about two weeks to com- 

 pletely harden. Sections thus prepared show the structure of the 

 inner layers of the retina, and the course taken by the blood- 

 vessels (in retinas which contain them), but the rod and cone 

 layer and the outer nuclear layer are not so good. 



