CHAPTER IV 



AVENUES OF INFECTION 



The Skin. While certain parasites, molds and fungi may be 

 implanted on a healthy skin by contact, either direct or indirect, there 

 is no known bacterium which will penetrate the healthy, unbroken 

 cutaneous covering of man under natural conditions. When pus bac- 

 teria are vigorously rubbed into the skin, especially when incorporated 

 in a salve, impetigo, furunculosis and even abscess formation may 

 result. Experimental infection of the lower animals has been induced 

 in a similar manner with plague, glanders, anthrax, tuberculosis and 

 recurrent fever. The plague bacillus may penetrate the unbroken and 

 unshaven skin of the guinea-pig and cause general infection. The 

 protection afforded by the skin is wholly mechanical. Infection 

 through the skin may result: (a) from the bites of animals, as rabies 

 from the bite of the dog; (b) from the bites of insects, as malaria and 

 yellow fever, transmitted by mosquitoes, and plague and other dis- 

 eases transmitted by fleas and possibly by other insects; (c) from 

 wounds, as syphilis, tuberculosis, diphtheria, tetanus, pus infections, 

 et cetera. 



The Eye. Local infection of the conjunctiva is a common acci- 

 dent. Gonorrheal infection is the most common cause of ophthalmia 

 neonatorum. Primary anthrax, tuberculosis, diphtheria and syphilis 

 in the eye have been observed. Animals have been inoculated through 

 normal eyes with glanders, plague and rabies. 



The Nose. Notwithstanding the marked germicidal character of 

 the nasal secretions, this organ furnishes lodgment for many bacteria 

 and is the seat of primary glanders and leprosy. Flexner has induced 

 poliomyelitis in apes by inoculating the nasal mucosa with the filterable 

 virus, and a minimal quantity of a plague-bacillus culture placed in 

 the nose of a rat leads to general infection. 



The Mouth. The pavement epithelium of the normal mouth fur- 

 nishes a fairly good mechanical protection against the local introduc- 



