518 



THE RESPIRATORY SYSTEM. 



By the injection of tubercle bacilli alone and associated with streptococci into the 

 lungs of rabbits through the trachea, it has been possible to reproduce very closely the 

 lesions of pulmonary tuberculosis in man. 1 



If a small quantity of a pure culture of the tubercle bacillus in very minute flocculi 

 be mixed with a considerable quantity of salt solution and introduced into the lungs 

 of rabbits through the trachea a number of small areas of consolidation are produced 



which have the gross appearance of 

 miliary tubercles (Fig. 297). These 

 small areas of consolidation are com- 

 posed of epithelial cells and leuco- 

 cytes. After the development of 

 these cell masses, which may occur 

 within a few hours, they may remain 

 with little apparent change, or be- 

 come more or less infiltrated with leu- 

 cocytes, or become cheesy, or be sur- 

 rounded by a dense zone of small 

 spheroidal cells ; or small foci of new 

 tissue with more or less exudate, and 

 necrosis may form. 



When larger quantities of the 

 tubercle bacillus are introduced into 

 the lungs through the trachea large 

 areas of consolidation are formed 

 (Fig. 298), which may involve whole 

 lobes or whole lungs. 



Microscopically, these consoli- 

 dated areas are practically identical 

 with those which are found in man 

 in various forms of tuberculous bron- 

 cho-pneumonia. A later fibrous-tis- 

 sue development may occur, and 

 blood-vessels may be obliterated. 



In the presence of the tubercle 

 bacillus alone the consolidated and 

 caseous areas- rarely soften and break 

 down so as to form cavities. If, how- 

 ever, after the tuberculous lesion of 

 the lung has been induced and allowed 

 The lung was injected with a considerable quantity of 

 tubercle-bacillus culture through the trachea, followed 

 after twenty-eight days by the injection of the broth cul- 

 ture of the Streptococcus pyogenes. Animal killed seven 

 days after the streptococcus injection. The specimen 

 shows large areas of consolidation with cavities. The 

 lesions resemble those of acute phthisis with cavities in 

 man. 



FIG. 299. EXPERIMENTAL TUBERCULOUS INFLAMMA- 

 TION IN THE LUNG OF A RABBIT, WITH THE FORMATION 

 OF CAVITIES. 



to continue for a number of days, a 

 culture of Streptococcus pyogenes be 

 introduced into the trachea of the rab- 

 bit, within twenty-four hours the 

 caseous areas often begin to soften. 

 The softening may begin at the cen- 

 tre, or may surround a central por- 

 tion of the necrotic mass. The softening is soon followed by absorption, and so cavi- 

 ties are formed of varying sizes and shapes (Fig. 299). 



It will thus be seen that in the rabbit a concurrent infection with the tubercle bacil- 

 lus and the streptococcus has an important bearing upon the breaking down of lung 

 tissue which leads to the formation of cavities. While it would not be wise to assume 

 from these experiments on the rabbit that a similar condition is always present when 

 cavities form in man, we have seen that in fact a similar concurrent infection in man in 

 acute phthisis actually does often exist. 



1 Prudden, New York Medical Journal, July 7th, 1894. 



