The type of the pneumonic process, as well as the invading organism, has varied widely in different localities. From the foregoing brief survey, it will be seen that before the associations suggested above can be proven, much more definite evidence must be presented.
An attempt has been made to correlate the bacteriological findings in this series with the distribution and type of pneumonic process. These are tabulated in Table III. It will be seen at a glance that no relationship is demonstrable between the type of single or associated organisms and the distribution of the pneumonia, whether it is lobar, pseudolobar, peribronchial or lobular and whether acute fulminating, necrotizing or organizing. (See Table No. III.)
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.