The question of a causal relation of the bacteria in gassed lungs to the pneumonia present cannot be regarded as decided. It may be said that:
1. The appearance of gassed lungs with pneumonia is very similar to the pneumonia of known bacterial origin.
2. In a few cases the type of pneumonia found coincides with the reported cases of so-called "chemical pneumonia," which is characterized by a preponderance of epithelial cells in the exudate.
3. Gassed lungs are not sterile but show highly varying numbers of bacteria.
4. The bacteria are not intracellular and are not present in large numbers in the majority of cases.
The arguments for and against a causal relationship between the bacteria and the pneumonia may be summed up as follows:
1. Against a Causal Relationship
a. The early appearance of pneumonia after gassing.
b. The occurrence of pneumonia with very small numbers of bacteria present.
c. The fact that very few bacteria are engulfed by leucocytes in gassed lungs, whereas large numbers are present in the non-gassed pneumonias and are conspicuously intracellular.
2. In Favor of a Causal Relationship
a. The presence of bacteria in any numbers.
b. The picture of broncho-pneumonia presented is similar to broncho-pneumonia of known bacterial origin.
c. Pneumonias characterized by large numbers of epithelial cells in the exudate (so-called "chemical pneumonia") occur in animals that were never gassed or subjected to other irritating substances in any way.