ANTISEPTICS— PAST AND PRESENT 43 



The folloA\dng' modes of infection merit consideration : 



1. Infection by Air. — Aerial infection was recot>nized 

 even in prescientific periods. The Listerian principles 

 and the carbolic spray were directed against this mode 

 of infection, and the air was regarded as containing 

 the germs of pntrefaction, which were capable of setting 

 up septic processes in wounds and their secretions. This 

 view has been considerably modified in the present day. 

 Experiments have demonstrated that the greater num- 

 ber of bacteria present in the air are non-pathogenic, 

 that germs exist in the atmosphere only in the form of 

 dry dust, that air perfectly freed from dust is harmless 

 to wounds, and when the air is kept still, wound infec- 

 tion rarely takes place through the atmosphere. But 

 when we consider the surroundings of horses, the dust 

 raised from a straw bed and during the process of clean- 

 ing the stall, we must admit the possibility of infection 

 by air containing dust. Indeed, some observers state 

 that they have found cocci closely related to the pyogenic 

 varieties, and sometimes actually belonging to that class, 

 in atmosphere dust, especially when the air is moist. 



2. Infection by Water. — Infection by means of the 

 water used occurs unless this fluid is sterilized by boil- 

 ing or a germicide is added thereto. Ordinary water 

 contains a large number of bacteria, usually many hun- 

 dred thousand per cubic centimeter. 



3. Miscellaneous Sources. — Other modes of infection 

 include infection from the skin of the patient, from the 

 hands of the surgeon or those of his assistants, from 

 instruments, sponges or their substitutes, ligatures and 

 sutures, dressing materials, vessels or utensils, syringes, 

 and in other ways. 



Circumstances Predisposing to Infection 



Among the factors which render a given infection 

 more likely to prove harmful is excessive injury to the 



