Pathogenesis 451 



monia results from the injection of cultures into the trachea of sus- 

 ceptible animals. A very interesting review of the literature of the 

 experimental aspects of the subject, embracing 198 references, will 

 be found in Wadsworth's paper upon "Experimental Studies on the 

 Etiology of Acute Pneumonitis."* 



The final proof that true pulmonary consolidation, i.e., pneumonia, 

 can be produced experimentally by cultures of the pneumococcus is 

 to be found in a paper byLamarandMeltzer.f These investigators 

 etherized dogs, kept the mouth open by means of a large 

 wooden gag, drew the tongue forward by means of hemostatic 

 forceps, and then, seizing the median glosso-epiglottic fold, 

 pulled it forward so that the posterior aspect of the epi- 

 glottis presented an inclined plane. Into this concavity one end 

 of a tube is placed. Under the protection of the left index- 

 finger the tube was directed into the larynx and pushed down 

 slowly and gently through the trachea until a resistance was met 

 with. The inner end of the tube was then found to engage in a 

 bronchus usually the right bronchus. A pipette containing a liquid 

 culture of the pneumococcus was next attached to the external end 

 of the tube, and by means of a syringe the culture (about 6 cc.) was 

 injected into the bronchus. The syringe was then removed, the 

 piston withdrawn, and the syringe again attached to the pipette. By 

 the injection of air the culture was driven deeper into the bronchi. 

 The tube was then clamped and withdrawn and the animal released. 

 By these means experimental pneumonia, with the typical consolida- 

 tion and lobar distribution, was produced in 42 successive cases. The 

 course of the inflammatory disturbance thus produced was rapid , and in 

 one case nearly complete consolidation had occurred in seven hours. 



Lesions. The lesions of croupous pneumonia of man are almost 

 too well known to need description. The distribution of the disease 

 conforms more or less perfectly to the divisions of the lung into 

 lobes, one or more lobes being affected. An entire lung may be 

 affected, though, as a rule, the apex escapes consolidation and is 

 simply congested. The invaded portion of the lung is supposed to 

 pass through a succession of stages clinically described as (i) con- 

 gestion, (2) red hepatization, (3) gray hepatization, and (4) resolu- 

 tion. In the first stage bloody serum is poured out into the air-cells, 

 filling them with a viscid reddish exudate. In the second stage this 

 coagulates so that the tissue becomes solid, airless, and approxi- 

 mately like liver tissue in appearance. The third stage is charac- 

 terized by dissolution of the ery throcy tes and invasion of the diseased 

 air-cells by leukocytes, so that the color of the tissue changes from 

 red to gray. At the same time the coagulated exudate begins to 

 soften and leave the air-cells by the natural passages, and the stage 

 of resolution begins. 



* "Jour. Amer. Med. Sciences," 1904, cxxvn, p. 851. 

 t "Jour. Exp. Med.," 1912, xv, No. 2, p. 133. 



