38 INFECTION 



carrier, " Typhoid Mary" a cook, is known to have infected 26 

 persons. Such persons because of their apparent innocence 

 might be called " hidden carriers." They have been found trans- 

 mitting dysentery and poliomyelitis as well as the above typhoid 

 fever, and, judging from the continued existence of the exanthe- 

 mata in cities, it may be that we shall find such persons harboring 

 the virus of varicella, mumps and pertussis. 



Local Immunity to Infection. There is evidently more resistance 

 offered by the liver against invasion than by the peritoneum. It 

 is not likely that a man would contract typhoid through skin 

 infection, nor is it probable that he would contract tetanus by 

 swallowing tetanus bacilli, but the reverse of these conditions 

 certainly produces infection. 



Infection may be caused from without the body, or from within. 

 Lockjaw, sepsis, hydrophobia, or anthrax may follow injuries from 

 rusty nails, splinters, weapons, unsterile fingers, or instruments. 

 Personal intercourse, bites, kisses, sexual intercourse, association 

 with persons suffering from exanthematous or contagious diseases 

 may transmit disease. 



Winslow has found colon bacilli upon 9 percent of the hands he 

 examined. Tubercle bacilli have been found on the hands of the 

 non-tuberculous. Some organisms, notably the smegma bacillus, 

 pyocyaneus bacilli and cocci resembling the white pus former, may 

 be said to be normal inhabitants of the skin. 



The bites of insects that are intermediate hosts of infectious 

 agents (plague bacilli, malarial organisms, etc.) are sources of 

 infection from without, as is also the ingestion of infected food or 

 water. 



Infection from within may be caused by the migration of bac- 

 teria from the skin inwards, or from any of the mucous membranes, 

 on which, and in which many pathogenic bacteria at all times may 

 be found. 



Bacteria from the mouth, stomach intestines and the rectum 

 may invade the tissues and the blood under certain conditions. 



