88 INFECTION 



bacteria into the deeper tissues. The greater number of local surgical 

 infections result from the entrance of bacteria into lesions of the skin, 

 although these lesions may be so small as to escape notice. 



Certain parasites are capable of producing direct action on the skin 

 without previous existing injury, and especially upon the mucous mem- 

 branes, where moisture and higher temperature are more favorable to 

 bacterial growth. For example, a few of the higher fungi, such as 

 Microsporon, Achorion, and Trichophyton, seem able to establish 

 themselves in the superficial cells and invade the deeper tissues through 

 the hair-follicles; staphylococci may reach the roots of hair-follicles 

 and sweat-glands and set up suppurative conditions; diphtheria bacilli 

 may lodge directly on the intact mucosa of the upper air-passages and 

 cause local necrosis and general intoxication; cholera bacilli may have a 

 similar effect upon the intestinal mucosa; the Koch- Weeks' bacillus 

 and the gonococcus may produce severe inflammation of an intact 

 conjunctiva, etc. 



2. The respiratory organs commonly afford admission to certain 

 microorganisms. The nose may be the seat of local infection with 

 Bacillus influenzae, Micrococcus catarrhalis, Bacillus diphtheriae, and 

 other bacteria; it may be the entrance point for meningococci and the 

 virus of anterior poliomyelitis. Similarly, the entrance of such unknown 

 infectious agents as those of scarlet fever, measles, and smallpox can 

 best be accounted for by assuming that they were inhaled and later 

 entered the blood; there is much clinical evidence to support the belief 

 that the contagium of scarlet fever is present in the discharges of the 

 upper air-passages of persons suffering from that infection. 



Whether or not tuberculosis of the lungs is the result of the inhalation 

 of tubercle bacilli is a much-disputed point, but it cannot be denied that 

 this theory most readily accounts for the far greater frequency with 

 which tuberculosis affects the lungs than it does other organs of the body. 



Pneumonia, caused by the pneumococcus of Weichselbaum, probably 

 results from the direct inhalation of one of the various types of pneumo- 

 cocci, and bronchopneumonia of children is certainly chiefly inspiratory 

 in origin. 



3. The digestive tract may be the portal of entrance of many in- 

 fections. The mouth usually harbors various fungi and bacteria,which may 

 produce local infections, and either directly or indirectly cause caries 

 of the teeth. The putrefactive changes they may produce is being 

 generally recognized as having an important bearing on the causation 

 and symptomatology of several infections, and a carious tooth has been 



