NERVE TERMINATIONS IN LUNG OF RABBIT 109 
The individual nerve endings spread over a relatively large 
area of epithehum. The termination illustrated in figure 1 
is represented as viewed somewhat obliquely so that the relative 
thickness of the epithelium in which it lay could not be indicated 
in the figure. The greatest breadth of this termination is about 
125 » and its length about 150 u. As will be noted in the figure, 
the main nerve fiber breaks up into seven principal branches, 
which in turn subdivide into secondary and tertiary twigs. All 
are studded with varicosities of varying size and form, and the 
tip of each of the terminal twigs is formed by a small knob-like 
enlargement. These terminal twigs pass between the cells of 
the columnar epithelium. Many approach the surface of the 
epithelium, but most of the twigs appear to end between the 
_ epithelial cells. These large, intricate nerve terminations 
resemble in many respects the endings found by Wolff (02) in 
the frog’s lung, with the difference that those described by Wolff 
were found in the interalveolar walls. 
The most characteristic position in which sensory endings are 
found in the rabbit’s lung is in the area of epithelium which lies 
between the bronchi of the various orders at the point of division 
of the bronchi. The plexiform nerve termination is situated at 
or near the apex of the point of epithelium in the crotch formed 
by the branching of the bronchial divisions. The endings 
which occur in the larger bronchial branches are of relatively 
larger size than those which are present in the epithelium of 
the lesser divisions. There does not seem, however, to be any 
difference in the size or appearance of the nerve fibers which 
lead to these terminations, no matter where located. With 
the methylene-blue stain they all show varicosities of varying 
size and form. ‘These fibers are given off from the nerve bundles 
which run roughly parallel with the bronchi. In many instances 
they may be traced individually for considerable distances before 
terminating in the epithelium (figs. 4 and 5). On reaching the 
epithelium they break up into a network which interlaces among 
the epithelial cells, very much in the same manner as the larger 
endings, above described, in the primary bronchi. The plexus 
thus formed possesses numerous varicosities, the larger of which 
