The Avenues of Infection 65 



The nose constantly receives enormous numbers of bac- 

 teria in the dust of the inspired atmosphere. These organ- 

 isms are too numerous and too various to mention, and 

 might, indeed, comprehend the entire bacterial flora. But 

 in spite of the large numbers of organisms received, the nose 

 retains scarcely any, its mucous membranes seeming to be 

 provided with some means of disposing of the organisms. 

 Thompson and Hewlett* performed an interesting experiment 

 to show this destructive action. Selecting the surface of one 

 of the turbinated bones, they spread a culture of Bacillus pro- 

 digiosus upon it, and then transplanted from the surface at 

 frequent intervals during a period of two hours. Cultures 

 made within five minutes showed confluent colonies of the 

 bacteria, but as time went on, the colonies became less and 

 less numerous, until after two hours no more were found, 

 all of the bacteria applied to the nose having been destroyed. 

 These experiments confirm the opinion of Wurtz and Ler- 

 moyez that the nasal secretions possess germicidal powers. 

 For these reasons the nose has no permanent parasitic flora. 



The larynx and trachea contain very few bacteria and 

 probably have no permanent parasitic flora. 



The lungs harbor no bacteria. A few micro-organisms 

 doubtless reach them in the inspired air, but the defensive 

 mechanisms soon dispose of them, and the normal lung is 

 almost invariably free of micro-organismal life. 



AVENUES OF INFECTION. 



The skin seems to form an effectual barrier against the 

 entrance of bacteria into the deeper tissues. A few higher 

 fungi Trycophyton, Microsporon, Achorion, etc. seem 

 able to establish themselves in the superficial layers of the 

 cells, invade the hair-follicles, and so reach the deeper 

 layers, where morbid changes are produced. The minute 

 size of the bacteria makes it possible for them to enter 

 through lesions too small to be noticed. Garre applied a 

 pure culture of Staphylococcus pyogenes aureus to the skin 

 of his forearm, and found that furuncles developed in four 

 days, though the skin was supposed to be uninjured. Bock- 

 hart moistened his skin with a suspension of the same organ- 

 ism, gently scratched it with his finger-nail, and suffered 

 from a furuncle some days later. 



The greater number of surgical infections result from the 



*" Lancet," 1896. 



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