450 SLONAKER. [Vol. XIII. 



the eye again made perfect by injecting into the vitreous 

 chamber with a hypodermic syringe enough 70/0 alcohol to fill 

 out the eye. It is kept 24 hours in each of the following 

 liquids: 80, 90, 95, loo/o alcohol, and a mixture of absolute 

 alcohol and ether (one part each). 



The eye is now well hardened and the front half may be cut 

 off, leaving the posterior half uninjured. After the hardened 

 vitreous humor is removed the retina is exposed to view. The 

 entrance of the optic nerve, area and fovea centralis, if present, 

 and the larger blood-vessels will be easily seen. In many cases 

 the area is very indistinct and the blood-vessels wanting or so 

 meagre as to be invisible to the naked eye. 



When one wishes to section the eye, a window is cut in the 

 same plane of the desired sections and the hardened vitreous 

 humor carefully removed without injury to the retina or other 

 structures. It is then changed to celloidin. Best results are 

 obtained when three grades of celloidin are used: (i) very 

 dilute ; (2) less dilute ; (3) as thick as will run. It is allowed 

 to remain from four to six days in the first, six to eight days in 

 the second, and ten to fifteen days or longer in the third. It 

 is then mounted on a block and cut in 80/0 alcohol. In every 

 case when sufficient material was at hand sections were made 

 in vertical and horizontal planes. Serial sections were always 

 saved through the fovea, so that the central section could be 

 readily distinguished. Sections were stained in hasmatoxylin 

 and eosin and mounted in balsam. 



In order to demonstrate more quickly the presence or 

 absence of an area or fovea centralis, the whole head of small 



Fig. 2. — Snow-bird (Junco hyemalis) 3/i. 

 f. Fovea centralis. N. Nerve entrance. P- Pecten. 



