IMMUNITY AGAINST MICROBES. 109 



Joseph Lister was the first to draw attention to that fact — that, 

 should the skin remain intact^awound of the lung rarely becomes 

 septic. Moreover, the elegant researches of Tyndal, Gunning, 

 Straus and H. Dubreul, and Straus^, prove that expired air 

 contains no microbes — that is, has been filtered in the lungs. 

 Other investigations have demonstrated the fact that the germs 

 stick to the moist surfaces of the upper air-passages, and that 

 very few only are carried into the lungs. Doubtless some are 

 carried into the alveoli, just as carbon-particles are carried 

 there. 



M. Tschistowitsch^ has lately shown what becomes of micro- 

 organisms which have been introduced into the lungs. He 

 found that micro-organisms Avhich are non-pathogenic for the 

 animal used, are at once attacked by the phagocytes of the lung 

 which swallow, digest, and destroy them ; the safety of the 

 animal being therefore dependant on the efficient action of 

 these cells. It follows that the bacilli which are carried by 

 the stream of air into the lungs, must at once be seized upon 

 and destroyed by these phagocytes. The fact that the lung 

 consists of a number of small aseptic cavities can thus be readily 

 explained. 



Having now studied the functions of wandering mesodermic 

 cells in healthy animals, let us see how these same cells react 

 when micro-organisms find their way or are artificially intro- 

 duced into an animaPs tissues. 



' JTor the literature on this subject see Straus, ' Anu. de I'Institut Pas- 

 teur,' 1888, p. 181. 



^ Tscliistowitscb, loc. cit. 



