IMMUNITY. 163 



bacteria) ; the blinking which occurs regularly a few times in a min- 

 ute, which in conjunction with the lachrymal moisture, throws out 

 again mechanically the already landed bacteria ; and finally, the bac- 

 tericidal effect of the tears destroys the balance of the invaders. 

 Or let us take the respiratory organ from the larynx down to the 

 respiratory tissue, including the corresponding lymph glands. . . . 

 Through this path the outside world stands in an intimate relation 

 with the interior of the body ; inasmuch as the air column is sepa- 

 rated from the lymphatics and capillaries of the lungs merely by a 

 single layer of the very thin epithelium of the air cells. Even the 

 serous cavities are separated from the lymph spaces by thicker lay- 

 ers. This arrangement is, of course, indispensable for the proper 

 exchange of the blood gases with the air. But what prevents the 

 bacterial invasion of the interior of the body by this open and direct 

 way? Moreover most of the writers agree that trachea, bronchi 

 and lung tissue of healthy animals are entirely sterile. In a num- 

 ber of rabbits under morphine anesthesia I found all these parts to 

 be sterile. If one vagus or a laryngeal branch was cut, then the upper 

 part of the trachea contained bacteria, but not the lung. When 

 both vagi were cut, then of course the lungs too were invaded. 

 Jundell reported recently that by means of a special device he was 

 able to test the human trachea, and found that in the majority of 

 healthy cases the region below the glottis proved to be sterile. What 

 protects this path? In my opinion the result is accomplished by the 

 cooperation of the following factors : The tortuous part of the res- 

 piratory path lying above the glottis removes perhaps the greatest 

 part of the bacteria contained in the inspired air column, and the 

 remaining number is, under normal conditions, just small enough to 

 be disposed of by the fectors present below the larynx. Bacteria 

 which pass the glottis are either carried back outside of the glottis 

 from the trachea and the bronchi by the steady movements of the 

 cilia of the epithelium, or, if the germs are carried in the center of 

 the air column down to the air cells, they quickly penetrate the thin 

 epithelial layer and are immediately within the reach of the lymph 

 glands, which take good care of them. ... In connection with 

 the respiratory path, I would like to recall here the interesting fact 

 that both canals which lead farthest to the innermost of the body, 

 that is, the respiratory and the female genital canal (which latter 

 terminates in the peritoneum), have ciliated epithelium, the move- 

 ments of the cilia being outward, and are, as far as the epithelium 

 extends, entirely or nearly sterile." 



Some of the factors which lead to immunity in the infectious dis- 

 eases pertain to the animal organism, while others are due to limita- 

 tions of the capability of growth on the part of the infecting agents. 

 For instance, but few if any of the pathogenic bacteria are able to 

 penetrate the unbroken skin, and infection through this avenue can 



