68 Infection 



blow-pipes, catheters, syringes, dental instruments, etc. — may serve 

 to transfer disease-producing organisms from one person to another 

 who might otherwise never come in contact with them. 



Attention should be called to the facility with which the diseases 

 of childhood may be spread through the thoughtless or ignorant 

 custom of many adults and children of using handkerchiefs, napkins, 

 forks, cups, spoons, etc., in common; in having wash-rags, towels, 

 hair-brushes and combs in common; cultivating the habit of putting 

 lead-pencils, etc., in the mouth, and then passing them on to others 

 who will do the same, and to many other relations of every-day life by 

 which infectious agents may be spread. ■ Scarlatina, measles, mumps, 

 acute anterior poliomyelitis, ophthalmia, tuberculosis, ringworm, 

 fevers, syphiUs, etc., may all be spread through such means. 



Suctorial insects seem occasionally to act as the medium by which 

 micro-organisms withdrawn in blood from one person may be in- 

 troduced 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 trypanosomiasis; the tick, of relapsing fever, the louse of 

 tj^hus fever, etc. 



Endogenous infections arise through the activity of micro-organ- 

 isms habitual to the body. They indicate morbid conditions of the 

 body by which the defensive mechanisms are disturbed, so that or- 

 ganisms harmless under normal conditions become invasive. 



All normal animals are presumably born free of parasitic micro- 

 organisms, 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-organisms, 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 un- 

 avoidable contact with surrounding objects determines that a variety 

 of organisms shall adhere to it. Of these, we can differentiate be- 

 tween forms whose presence is unexpected and temporary; others 

 whose presence may be expected; and still others whose presence 

 is invariable. 



Elaborate investigations upon the bacterial flora of the skin have 

 been made by Unna;* Mittman,t who studied the finger-nails, under 

 which he found no less than seventy-eight different species ;Maggiora, J 



* "Monatshefte fur prakt. Dermatol.," 1888, vii, p. 817; 1889, vin, pp. 293, 

 562; 1889, IX, p. 49; i8qo, X, p. 48s; 1890, XI, p. 471; 1891, XII, p. 249. 

 t "Archiv. £. path. Anat. u. Phys. u. f. klin. Med.," 1888, cxiii, p. 203, 

 t"Giornale della R. Society d'Igieha," 1889, Fasc. 5, p. 335. 



