TERMINALS OF HUMAN BRONCHIOLE - AAAS) 
To obtain a clearer picture of the terminal branchings, those 
represented in both models were projected upon a single plane, 
the projections being based partly on tracings of various sections 
used in the construction of the models, and partly on sketches 
of the smaller parts. The result obtained in the case of the 
model of the child’s lung is shown in figure 3. The stem marked 
1 is a non-respiratory bronchiole which was traced through sev- 
enty-four sections (2.22 mm.) to reach its origin from a bron- 
chiole with cartilage in its wall. Four dichotomies occurred in 
this distance. In the model of the adult lung three dichotomies 
occurred between the first respiratory bronchioles and the bron- 
chiole with cartilage in its wall. The stem (1) divides into two 
branches, only one of which (2) was followed; this was a respira- 
tory bronchiole, alveoli occurring on its wall. It in turn under- 
goes a dichotomy, only one limb of which (3) was followed, and 
then two additional dichotomies succeed in rapid succession, 
only one branch of each being followed. That followed from the 
last of these dichotomies (6) again divides into 7 and 8, these 
again into 9 and 10 and 11 and 12, respectively, but beyond this 
the branchings become irregular, and while it would be possible 
to interpret some of these divisions as dichotomies, there are 
others where the branching could be more accurately termed a 
trichotomy. In fact, the branching in some parts is so irregular 
that almost any ‘method’ might be read into it. The truth seems 
to be that, as the terminals are approached, no one system of 
branching is followed, but one edict is obeyed, i.e., that there 
must be no waste of space. 
Embryological investigation has shown that in the early devel- 
opment the branching is dichotomous, and apparently this is 
continued, with some modification in certain of the branches, 
until there comes a time when the small bronchioles are competing 
with one another for space, and then they branch or send out 
processes in any possible direction. This competition for space 
of the infundibula and alveoli, seen in the complicated inter- 
digitation of these elements from different respiratory bronchioles 
and in their varying form and size, is the most striking impression 
that one receives from a study of the models. An idea of the 
