106 The Philippine Journal of Science 1920 
artery. Those of the pulmonary veins communicate with those 
of the pleura. Valves are present in the deeper lymphatic 
system, which open toward the hilum, while those on the peri- 
phery drain toward the pleura. No lymphatics are found distal 
to the alveolar ductules. 
The masses of lymphoid tissue in the lungs are important, 
for they are very often the starting point of tuberculosis. Nodes 
are found along the larger bronchi but not in the region of 
the respiratory bronchi or alveolar ductules; they are always 
found in the angle of dividing bronchi. Small masses of lymph- 
oid tissue have been demonstrated in the walls of the veins, 
also in the angle at the junction of two veins; it has also been 
found in the pleura around the radicles of the pulmonary ar- 
tery. It is without doubt true that the lymphoid tissue is the 
primary focus of infection in tuberculosis, the phagocytes having 
carried the bacilli to this region from the smaller air spaces. 
Having a knowledge of the arrangement of the air spaces 
and knowing that the secondary lobules are separated from 
each other in well-defined areas, we can easily distinguish 
between the primary and the secondary lobules ; you will readily 
see that this arrangement of pulmonary tissue under certain 
pathological conditions, more particularly tuberculosis, will occa- 
sion an increase of density on a roentgenogram which, if viewed 
from the proper angle, will be more or less triangular in shape. 
This is what is known as the “Dunham fan;” it will usually be 
found at the end of a trunk composed of a bronchiole, blood ves- 
sels, and lymphatic and connective tissue. The size of the fan 
is determined by the number of lobules involved. The type of 
pathology will also influence the character of the density for, 
should it be an advanced condition, we will have a diffuse den- 
sity with fans showing here and there, many of them irregular 
in size and shape. Thus the characteristic marking of a plate 
of pulmonary tuberculosis consists of fan-shaped density with 
the apex toward the hilum, and the base toward the pleura, the 
apex being connected with the hilum by a heavy trunk. If we 
have two or more such areas of differing density, we will see 
the picture of tuberculosis, the greatest density indicating the 
oldest lesion. There may be great variation of density in the 
fan, varying from radiating lines (known as linear markings) 
to a heavy blotting-out effect. The most striking characteristic 
lies in the varying degree of change in the different trunk 
groups, for one trunk may be involved while the one next to it 
may be absolutely clear. It is very striking that in the early 
