Jones — Nestling Feathers. 5 



ally difficult and unsatisfactory. The corrosive sublimate had a strong ten- 

 dency to make the tissues brittle. 



With the alcohol-formalin solution, a fixation of six hours was always 

 sufficient, and four hours would often suffice. Washing out of the formal- 

 dehyde was effected by the use of 70% alcohol, changing about ten times. 

 Various combinations of alcohol and formaldehyde were used, but the form- 

 ula given proved the most satisfactory. 



The only satisfactory method for clearing and infiltration with paraffin 

 was the chloroform method. Tissues were first cleared in chloroform and 

 then placed in a saturated solution of paraffin in chloroform two to five days, 

 according to the thickness of the tissue. They were then transferred to 

 melted paraffin for six to ten hours, and imbedded in hard paraffin (melting 

 at 52° C). 



Serial sections were cut one to ten micra thick, mostly three tnicra. 

 Complete series "of all but the latest ^stages were easily obtained. For the 

 thinnest sections, a temperature between 55° and 60° F., while cutting, was 

 found necessary, and the best results were always obtained at temperatures 

 not much above 60°. 



For affixing sections to the slide a combination of the Mayer's albumen 

 fixative with the water method was found the most satisfactory, but many 

 times, particularly with the larger specimens, the albumen fixative was un- 

 necessary. With the latest stages, where many elements were cornified, it 

 was necessary to paint the dry slides, bearing sections, with a film of very 

 thin celloidin solution to insure the retention of the sections during sub- 

 sequent processes. These cellodin films were sometimes detached from the 

 slide for quicker and more accurate staining. 



Various stains were used, the two giving the most certain and satisfac- 

 tory results being Delafield's hzematoxylin and the Heidenhain iron hnem- 

 atoxylin. Delafield's haematoxylin was used very dilute in distilled water — 

 a pipette full of the stain to about 150CC of distilled water, the exact pro- 

 portions being unimportant. Slides left in this weak stain for 48 hours were 

 always overstained, and reduction of the stain was accomplished by the use 

 of weak acid alcohol. A saturated solution of eosin in 95% alcohol was used 

 in the process of dehydration for double staining, to bring out the cornifying 

 elements. 



Feather germs were sectioned longitudinally, transversely and obliquely 

 for all stages, and the sections were mounted in Canada balsam. A great 

 deal of material was also teased on the slide and mounted in glycerine tem- 

 porarily for immediate study. It was usually necessary to stain such material 

 before teasing so that the structures could be seen. Dry nestling feathers 

 with downy tips were dehydrated and cleared, and then mounted whole in 

 Canada balsam for study of the entire feather. 



For the earlier stages of the definitive feather it was necessary to cut 

 out pieces of the skin containing the desired material. All attempts to pull 



