STRONG: DEVELOPMENT OF COLOR IN DEFINITIVE FEATHER. 149 
Material was kept in the picro-sulphuric solution for about five hours 
and then transferred to 70% alcohol followed by 90%. It usually took 
one to two weeks with several changes of alcohol to remove all traces 
of picric acid. A fixation of three hours was found sufficient for 
Hermann’s fluid and the usual methods of washing and hardening 
followed. 
Dehydration was accomplished by immersion in absolute alcohol for 
at least twenty-four hours. 
For clearing and infiltration with paraffin, I have found the chloro- 
form method especially satisfactory ; it was the only successful medium 
for cornified portions of the feather when anything like complete series 
were desired. I have found it particularly good in preparing material 
for sections of dry feathers. I have often secured almost perfectly 
complete series with it, whereas with xylol, or cedar oil, only occasion- 
ally would a section remain in the paraffin ribbon. 
Feather germs were left in melted paraffin two to five days and were 
then imbedded in hard paraffin (135° F.).’ Dry feathers were, in 
ordinary cases, dropped into chloroform for a few hours and then 
transferred to melted paraffin for about twelve hours. 
Serial sections were cut with a Minot-Zimmermann microtome 3} to 
10 micra thick, mostly 34 or 62 micra. Also a few sections at the proximal 
end of the feather germ were cut 2 micra thick by means of the Minot 
microtome having Zimmermann’s improved feeding attachment. I 
found it necessary to have the temperature as low as 60° F., and each 
section was cut with a very slow motion of the object carrier. For 
almost all purposes, however, sections 34 micra thick are thin enough. 
Sections of the cornified portions of the feather germ are very elastic 
and tend to curl and spring from the paraffin ribbon, especially when 
the sections are as much as ten micra thick, but with the methods 
described above fairly complete series were obtained. 
Mayer’s albumen fixative was used successfully for affixing sections to 
the slide; but with osmic-acid material it was found necessary to 
spread, in addition, a thin film of celloidin over the sections, immediately 
after the immersion in alcohol which followed the removal of paraffin 
with xylol. This celloidin film held the sections securely in position and 
did not interfere with subsequent work. 
A number of stains were tried, but by far the most satisfactory 
were (1) for material fixed in picro-sulphuric a double stain, viz. 
1 A mixture of hard paraffin with about 5% of resin was suggested by Professor 
G. H. Parker and was used with some success for dry feathers. 
