354 Pulmonic Interstitial Emphysema 



very rapidly. We must assume alveolar-base rupture, since that is the only way 

 air can possibly leak from the lung air spaces into the connective tissue unless 

 it be through the walls of the bronchi and bronchioles, and there is no evi- 

 dence of that. It should be frankly admitted that we do not know the details 

 of the morphological changes going on in the interior of the lungs in any of 

 these natural overstrain cases; and it may well be that, inider these abnormal 

 conditions, certain areas of the lung are likely to expand unduly and thus to 

 suffer alveolar-base rupture. Accordingly, there may be, even here, local areas 

 of overinflation. If this is so then the mechanics of PIE production would be 

 comparable to those obtaining in the local alveolar-base overstrain cases. 



The literature on submarine escape and analogous events is growing, and 

 only a little of it has been here referred to. We may confidently look for more 

 enlightenment on obscure points in the near future and, as knowledge un- 

 folds, the role of functional anatomy in facilitating progress in pathological 

 science will be increasingly useful. The important practical point is that air 

 should be diagnosed whenever present and released by aspiration whenever 

 it is causing airblock. 



Artificial Overstrain Cases.— \x. is always difficult to classify the items in a 

 new subject like the pneumonopathies herein dealt with, and it is quite pos- 

 sible that the PIE resulting from sudden and unorthodox submarine escape 

 should appear under the heading of the artificially induced cases rather than 

 those arising from "natural" living conditions. However that may be, it is 

 certain that the lung-blast cases belong in the artificial group. 



Lung 5/rt5f.— Although people have been experiencing serious injury and 

 death from explosions for a long time, yet it is only recently that attention 

 has been given to the changes in the lung shown by these catastrophies. There 

 are already many articles on the subject to be found in the literature, but here 

 we shall be able to refer to only a few of them. Although the effect of bomb 

 explosions on the lung (as on the body as a whole) varies from total disin- 

 tegration to relatively slight injury, we are most of all concerned with those 

 cases which survive and in which there is a chance of doing something to aid 

 recovery from PIE and its sequelae. That PIE is caused by lung blast there 

 is no doubt,"* for autopsy findings in the victims show it. There are, too, clinical 

 observational signs in human subjects and X-ray pictures in experimental 

 animals which point to its existence, and syndromic recordings typical of air- 

 block are already to be found in the literature. 



Lung blast is a special phenomenon composed of two phases, compression 

 and decompression. The time of each phase is very brief, and in this respect 

 the etiology differs from other cases of PIE that we have been reviewing. The 

 severity of the injury varies, of course, with the violence of the explosion and 

 its proximity. For an analysis of its physics, etc., reference must be made to 

 other sources. The effect of the compression wave is like that of a sudden, 

 sharp, but nonpenetrating and diffuse blow struck against the chest wall."" It 

 does not enter via the trachea.™ The ribs are not usually fractured. The intra- 



