COLLECTION, SELECTION AND PREPARATION OF MATERIAL 



9 



Diseased or injured eyes are also of no use in 

 this investigation. 3. After skinning, sever 

 the head from the body by decapitation close 

 to the base of the skull. 4. Label the head 

 by tying a string — to which a label is at- 

 tached — securely through the nostrils on 

 the beak. This label should bear, written 

 distinctly with a hard pencil, both the common 

 and zoological name of the bird, the date and 

 locality of collection, as well as the name and 

 address of the collector. Heads of the same 

 species should be numbered serially (1, 2, 3, 

 etc.). 5. The foregoing operations should 

 occupy as brief a time as possible. The head 

 should then be immersed in a quantity of 

 fresh Perenyi's fluid equal to twenty times 

 the volume of the head. Fruit jars are con- 

 venient containers for this purpose. For- 

 mula of Perenyi's Fluid: 10% nitric acid in 

 clean water (10 acid to 90 water), 4 parts; 

 95% (commercial grain) alcohol, 3 parts; 

 0.5% chromic acid in clean water (grm. 0.50 

 acid to 100 cc. water, 3 parts. After a few 

 minutes this mixture turns a violet color. 

 It may be kept in bulk indefinitely if well 

 corked. 6. Leave the heads in Perenyi's 

 fluid until the hardest bones of the skull be- 

 come soft and pliable when touched with a 

 scalpel. The time required will depend upon 

 the size of the head. The following periods 

 of immersion will usually be sufficient : Small 

 heads, as sparrow, robin, etc., 24 hours; me- 

 dium sized heads, as the crow, 36 hours; large 

 heads, as the owl, 48 hours ; extra large heads, 

 as the ostrich, 3 to 4 days. 7. After decal- 

 cification in Perenyi's fluid the heads should 

 be treated with the following percentages of 

 commercial grain alcohol. In each case use 

 approximately 20 volumes of the alcohol 

 solution to one volume of the head. The best 

 results are obtained by using fresh alcohol solu- 

 tion for each head. Leave the heads in each 

 of these alcohols for the same period they were 

 immersed in Perenyi's fluid. 70% alcohol is 

 made by mixing 70 volumes of 95% (commer- 

 cial grain) alcohol with 25 volumes of clean 

 water; 80% alcohol, made by mixing 80 vol- 

 umes of 95% alcohol with 15 volumes of clean 

 water; 95% (commercial grain) alcohol. 8. 

 After treatment with the last alcohol solution 



the heads may be packed in a fruit jar suffi- 

 ciently large to hold them, covered with 95% 

 alcohol and carefully sealed to prevent leakage. 



Should the eyeball lose its rotundity, or 

 "cave in" anywhere, the defect may be some- 

 times remedied by injecting 70% alcohol, by 

 means of a hypodermic syringe, into the 

 vitreous chamber. 



Prepared in this way the bones of the skull 

 and the sclerotic plates are so softened that 

 sections of them can readily be made, while 

 the walls of the eyeball are so hardened that 

 they can be bisected at the equator with a sharp 

 razor and the anterior segment removed, with 

 the cornea, lens and vitreous. The parts 

 behind, in the posterior half of the globe, 

 constituting the fundus ocidi, eyeground or 

 background of the eye, remain in situ and can 

 be readily examined. 



Although injection of the arteries of the 

 avian fundus is not as useful as in those eyes 

 in which there are retinal vessels, yet occa- 

 sionally the choroidal bloodvessels and (per- 

 haps) the pecten are affected by it and thus 

 rendered more visible. In that case prefer- 

 ably the gelatine-carmine mass of Ranvier is 

 injected by way of the carotid arteries. 



In examining macroscopically the posterior 

 segment of the eyeball a magnifying lens of 

 10 cm. focus may sometimes be used but the 

 unaided eye is generally satisfactory. 



On removing the hardened vitreous (by 

 means of a mounted needle) the grayish, 

 translucent retina should lie smoothly on the 

 choroid when the preparation is a success. 

 Retinal wrinkling occurs not infrequently in 

 some part of the eyeground, in which case it 

 may give rise to errors in determining the 

 presence or absence of some of the areas of 

 distinct vision, etc. A well preserved eyeball 

 furnishes satisfactory material for many years. 



For microscopic sections a window is cut in 

 the globe in the plane of the desired sections, 

 the vitreous removed without injury to the 

 choroid and retina and the cavity filled (by 

 immersion) with celloidin. However, as the 

 minutiae of this form of investigation is out- 

 side the scope of this work the writer must 

 refer the reader to laboratory textbooks on 

 the subject. 



