392 APPLICATION OF METHODS OF BACTERIOLOGY 



tory areas are in all important details identical with those 

 of true pneumonia in man. This experimentally-produced 

 pneumonia is not, however, clinically identical with pneu- 

 monia in man, as it is not accompanied by the crisis, nor 

 does one observe the sequence of local changes leading to 

 resolution that are commonly noticed in the course of pneu- 

 monia in man. Nevertheless, the results of this investiga- 

 tion justify the conception that pneumonia in man may 

 not, after all, be from the start a matter purely and simply 

 of the invasion of the lung by pneumococci, but rather that 

 for such invasion to be followed by the characteristic lesions 

 of the disease, there must first exist physical conditions 

 favorable to the massed or circuipscribed development of 

 the organism. In the light of Meltzer's studies one can 

 conceive that through one or another of many causes 

 exudations, non-specific in character, may occur in the 

 lungs, occlude terminal bronchi and, as in the experimental 

 cases, cause small cavities into which pneumococci, gaining 

 access, develop as in a closed space — and by the products 

 of their growth bring about progressive inflammation of 

 the tissues surrounding them. The experimental evidence 

 also suggests the view that pneumonia probably always 

 starts as such isolated patches which, by extension, coalesce 

 until finally larger areas or indeed whole lobes of the lungs 

 are involved. When this inflammation of the lung, with its 

 accompanying symptoms, have progressed for about a week, 

 the crisis may be expected, i. e., the distressing symptoms 

 become more or less suddenly relieved, fever begins to 

 decline, respiration is less difficult, and there are beginning 

 signs of changes in the diseased lung tissue, i. e., resolution 

 may set in. 

 These sudden changes for the better, so often observed 



