72 Infection 



dust of the inspired atmosphere. These organisms are too numer- 

 ous and too various to enumerate, and might, indeed, comprehend 

 the entire bacterial flora. But in spite of the large numbers of organ- 

 isms received, the nose retains scarcely any, its mucous membranes 

 seeming to be provided with means of disposing of the organisms. 

 Among those best able to withstand the destructive influences, and, 

 therefore, most apt to be found in the deeper passages, are the pseudo- 

 diphtheria bacillus, streptococci, pneumococci, staphylococci, Ba- 

 cillus pneumoniae (Friedlander), Bacillus subtilis and sarcina. A 

 complete review of the subject with references to the literature 

 has been made by Hasslauer.* 



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. 



AVENUES OF INFECTION 



The skin seems to form an effectual barrier against the entrance 

 of bacteria into the deeper tissues. A few higher fungi Tryco- 

 phyton, Microsporon, Achorion, etc. seem able to establish them- 

 selves 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 fore- 

 arm, and found that furuncles developed in four days, though the 

 skin was supposed to be uninjured. Bockhart moistened his skin 

 with a suspension of the same organism, gently scratched it with 

 his finger-nail, and suffered from a furuncle some days later. 



The greater number of surgical infections result from the entrance 

 of bacteria through lesions of the skin. It makes but little difference 

 to what depth the lesion extends abrasions, punctures, lacerations, 

 incisions the protective covering is gone and the infecting organ- 

 isms find themselves in the tissues, surrounded by the tissue lymph, 

 under conditions appropriate for growth and multiplication, provided 

 no inhibiting or destructive mechanism be called into action. 



The digestive apparatus is the portal through which many infec- 

 tions take place. The Bacillus diphtherias, finding its way to the 

 pharynx, speedily establishes itself upon the surface, producing 

 pseudomembranous inflammation there. Typhoid bacilli, dysentery 

 amoeba and bacilli, cholera spirilla and related organisms, finding their 

 way to the intestine, where the vital conditions are appropriate, take 

 up temporary residence there, to the injury of the host, who may 

 suffer from the respective infections. 



* " Centralbl. f . Bakt. u. Parasitenk. I. Abt. Referata," Bd. "xxxvn, Nos. 

 1-3, p. i, and Nos. 4-6, p. 97. 



