NERVE TERMINATIONS IN LUNG OF RABBIT 107 
It was found that twenty to twenty-five minutes was the 
optimum time for continuing the oxidizing of the stain in the 
lung tissue in this manner. The lungs were then quickly extir- 
pated and filled with 8 per cent cold ammonium molybdate, to 
which two to five drops of 1 per cent osmic acid were added 
per 100 cc. of the ammonium molybdate. The trachea was then 
ligated and the lungs immersed in a considerable quantity of the 
same mixture kept at a low temperature. This was allowed to 
act overnight. The ammonium molybdate was washed out by 
allowing the preparation to remain for an hour in running 
tap-water. The lungs were then filled with 95 per cent alcohol, 
which was changed several times within an hour, and also 
immersed in alcohol to bring about fixation and hardening of 
the tissues. This was followed by absolute alcohol for several 
‘hours or overnight. The lungs were then cut into pieces 2 to 4 
mm. thick, cleared in xylol, and embedded in paraffin. Some 
of the lungs were treated with 95 per cent alcohol immediately 
following the ammonium molybdate, without previous washing 
in water. These showed the atria and air spaces to better 
advantage, but many of the air passages were filled with a precip- 
itate which often obscured the nerve fibers. Sections were cut 
at 25 u to 100 w and mounted serially by the usual methods. 
Some were counterstained on the slide with aurantia. 
The pyridine-silver method also was tried on the lungs of 
several kittens, but with unsatisfactory results. 
SENSORY TERMINATIONS 
Sensory nerve endings occur in the epithelium of the primary 
bronchi, at the division points of the bronchi of the various 
orders and also in the walls of the atria. Careful examination 
of five pairs of lungs prepared by several modifications of the 
methylene-blue technique failed to reveal any indubitable 
nerve terminations resembling the sensory type in the walls of 
the air sacs or pulmonary alveoli. Many of the preparations 
appeared to be sufficiently well stained to warrant the expec- 
tation of finding such endings in the air sacs and alveoli if they 
are present. 
