The confusion which exists in associating different bacterial types with
well defined and characteristic anatomical lesions is true, not only for
the disease as it occurs spontaneously in man, but also for its
reproduction in experimental animals. A review of the literature teaches
that not all of the factors concerned in producing the different
anatomical types are known.
Pertinent experimental studies were reported recently by Blake and Cecil
from the Army Medical School in Washington. One cubic centimeter of a
very virulent pneumococcus (M. L. D. for a mouse in forty-eight hours
equals one-millionth of 1 cubic centimeter) inoculated in monkeys
through the skin of the neck into the trachea just beneath the larynx
has uniformly produced a lobar pneumonia, clinically as well as
anatomically the nearest experimental approach to spontaneous lobar
pneumonia of man. This work indicates, not only the possible importance
the species may play, but also points to the rôle of the infecting
organism which, when sufficiently virulent, incites a characteristic
reaction even when inoculated in a minimal quantity into the trachea as
distinct from the bronchioles or lung tissue.
Pneumonia unassociated with a simultaneous or preliminary incapacitation
of the mechanism of the upper respiratory tract, differs from the
pulmonary lesions encountered after measles, gas poisoning, influenza,
etc., and those experimentally produced by intrabronchial insufflations.
In the lobar type the virulence of the infecting organism, combined
perhaps with species variation,—implying as this does different
capacities for reaction on the part of the host,—seems to be the
fundamental principle. It remains to be determined whether other
organisms of equal virulence with that of the pneumococcus are capable
of producing characteristic anatomical reactions when inoculated in a
similar manner.
In the other group, where there is not only a free ingress to the
pulmonary parenchyma by the bacteria of the mouth, but where there is,
in all probability, also a simultaneous or preliminary pulmonary damage
furnishing a proper medium for relatively innocuous organisms, the
lesion of response will surely depend upon other factors as much as upon
the infecting organism. Among these obscure factors, the most important,
unquestionably, is the extent of the damage to the lung tissue before
the entry of the organisms, or simultaneously with it, into this area.
The systemic capacity to compensate also must be considered.
[Illustration:
FIG. LI. AUTOPSY NO. 194. A LUNG IN WHICH INFLUENZAL PNEUMONIA AND
PULMONARY TUBERCULOSIS ARE ASSOCIATED. THERE IS A CIRCUMSCRIBED,
OLD, TUBERCULOUS FOCUS IN THE UPPER LOBE. COMPARE FIGURES XXXIX AND
XL.
]