416 APPLICATION OF METHODS OF BACTERIOLOGY 



(resistance) through a variety of agencies, to a point that 

 enables the pneumococcus, hitherto present only in a com- 

 mensal relationship, to exhibit its pathogenic activities. 

 This is plausible, but that is all. There is nothing definite 

 in the way of experimental evidence to support it. 



The most satisfying explanation* of the beginnings of 

 pneumonia is that offered by the investigations of Meltzer 1 

 and his associates. They demonstrated that if fairly large 

 amounts (5 or 6 c.c.) of fluid cultures of pneumococci be 

 insufflated into the lungs of dogs, that many of the bron- 

 chioles became occluded as the result of the exudation 

 following such insufflations. The occlusion converts the 

 termini of those bronchioles, with their alveoli, into tiny 

 cavities. In such cavities the pneumococci develop and 

 produce irritating substances which in time bring about 

 more or less extensive inflammation of the lung tissues 

 round about them. The characteristics of these inflamma- 

 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 pneur 

 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 circumscribed development of 



Uour. Exp. Med., 1912, xv, 133. 



