50 INFECTION AND IMMUNITY. 



ganisms, or with tetanus bacilli,, may be derived 

 from ordinary earth or earth contaminated with 

 the dried excretions of animals. And in other 

 cases dried and pulverized urine or feces (typhoid, 

 cholera), or desiccated discharges from diseased 

 surfaces, from sinus and abscesses (tuberculosis, 

 erysipelas), may give rise to infected dust. The 

 skin may be an important source of infected dust 

 in the desquamative diseases (scarlet fever, measles, 

 smallpox), in that individual horny cells or groups 

 of cells laden with organisms may float in the 

 air with no great velocity in the movement of the 

 latter. 



The importance of dust infection is curtailed, 

 however, because of the slight resistance which 

 many microbes show against desiccation and the 

 germicidal action of light. Gotschlich classifies 

 micro-organisms regarding the likelihood of their 

 participating in dust nf ection as follows : 

 of ( a ) Organisms which are not capable of living 



Organisms. .,/. 6 .,.,.,. 1 _ . *T\ 



in dust as it is dried in the air, and hence never 

 (rarely might be better) can be disseminated 

 through dried particles (cholera, plague, gonor- 

 rhea, influenza). 



(b) Organisms which are capable of being car- 

 ried as dust for considerable distances by such 

 weak currents of air as ordinarily exist in dwell- 

 ings, and which, when once suspended in the air, 

 remain alive for a long time, and easily lead to 

 dust infection (pus cocci, pyocyaneus, meningococ- 

 cus, anthrax spores, tubercle bacilli and tetanus 

 bacilli) . 



(c) Organisms which, indeed, are resistant to 

 desiccation, but which are disseminated as dust 

 only through stronger air currents, such as occur 



