92 . INFECTION 



isms, and may yet escape infection, unless a small break in the surface 

 epithelium, in the form of a scratch or a needle-prick, is present. 



2. As has been previously stated, certain bacteria, notably the 

 diphtheria bacillus, by concentrating at one point, may lower the vitality 

 and cause necrosis of superficial cells of the mucosa lining the upper air- 

 passages, and in this manner induce a local break in the continuity of the 

 epithelial covering. Staphylococci may exert a similar action in the 

 depths of sweat and sebaceous glands, and, indeed, certain fungi, such 

 as the Trichophyton, Microsporon, and Achorion, may attack the 

 intact skin. While, therefore, solution of the surface coverings is a very 

 important source of many infections, it is not essential for the produc- 

 tion of all. 



3. Alterations of the surface discharges, either in quantity or in 

 quality, may permit bacteria to proliferate freely and produce sufficient 

 toxic matter to affect the surface cells, lower their vitality, and destroy 

 them, with the result that they may gain entrance to the deeper tissues. 

 When the secretions are diminished or altered, as, for example, the saliva 

 during a fever, unless the mouth is carefully and frequently cleansed, 

 it becomes putrescent with bacterial growth. Similarly catarrhal 

 gastritis, or any other factor tending to lower acidity of the gastric juice, 

 favors infection by this route. 



4. Not infrequently bacteria may gain access to the deeper tissues 

 or to an internal organ, and infection may occur without any recognizable 

 solution of continuity of the surface epithelium. In these hidden or 

 "cryptogenic infections" the entrance point of the parasites may be 

 healed over, or the infecting microorganisms may have been carried to 

 the circulating body fluids by the wandering cells. 



Not infrequently, in cases of tuberculosis of the cervical and mesen- 

 teric glands in children, there may be no signs whatever of local irrita- 

 tion in the fauces or in the intestine to explain the source of infection. 

 The tonsils are now strongly suspected, and indeed known to be, the 

 source of entry of bacteria causing several acute and chronic infections. 



The leukocytes, in their phagocytic activities, no doubt, play an 

 important role in the production of cryptogenic infections, especially 

 when an excessive number of pathogenic bacteria have congregated at 

 one point, and congestion, increased leukocytic infiltration, and a 

 lowered vitality of the tissues have occurred prior to the invasions of 

 microorganisms. Wandering cells are commonly found on mucous 

 membranes, gathering up various bacterial and cellular debris. They 

 may carry a virulent microorganism into the deeper tissues, and, al- 



