8o Infection 



Wounds inflicted by the teeth of animals, by weapons, by 

 implements, or by objects of various kinds, carry into the 

 tissues micro-organisms whose operations, local or general, 

 may variously affect the organism to its detriment. 



Contact with unclean objects of various kinds spoons, 

 knives, cups, blow-pipes, catheters, syringes, dental instru- 

 ments, etc. may serve to transfer disease-producing organ- 

 isms from one person to another who might otherwise never 

 come in contact with them. 



Suctorial insects seem occasionally to act as the medium 

 by which micro-organisms withdrawn in blood from one 

 person may be introduced into other persons so that they 

 become infected. The flea thus brings about the spread of 

 plague; the mosquito, of malaria; the tsetse fly, of trypano- 

 somiasis; the tick, of relapsing fever. 



Fomites, or objects made infective through contact with 

 individuals suffering from smallpox, scarlatina, and other 

 contagious or actively infectious diseases, become the means 

 through which the specific micro-organisms may be con- 

 veyed to the well with resulting infection. 



Endogenous infections arise through the activity of 

 micro-organisms habitual to the body. It indicates a 

 morbid condition of the body by which the defensive mechan- 

 isms are disturbed, so that organisms harmless under normal 

 conditions become invasive. 



All normal animals are born free of parasitic micro-organ- 

 isms, but it is impossible for them to remain so because of 

 the universal distribution of micro-organismal life. The 

 air, the water, the soil, and the food, as well as the associates 

 of the young animal, all act as means by which micro-organ- 

 isms, and especially bacteria, are brought to the surface and 

 cavities of its body, and but a short time elapses after birth 

 before it harbors the customary commensal and parasitic 

 forms. 



BACTERIAL TENANTS OF THE NORMAL HUMAN BODY. 



The skin and adjacent mucous membranes. The 



slightly moist warm surface of the skin is well adapted to 

 bacterial life, and its unavoidable contact with surrounding 

 objects determines that a variety of organisms shall 

 adhere to it. Of these, we can differentiate between forms 

 whose presence is unexpected and temporary ; others whose 



