1 62 PHARMACEUTICAL BACTERIOLOGY. 



construction whether private home, school, factory, sleeping car, office, 

 or street car. There is plenty of pure air and every individual should have 

 an ample supply, for pure air is one of the most potent factors in preven- 

 tive medicine. 



C. Heat. Heat is one of the best disinfectants known. Dry and moist 

 heat are used, both of which have been sufficiently treated in the preceding 

 chapters. Mere dryness is in itself a germ destroyer. Microbes require 

 moisture for their growth. Most bacteria (vegetative cells, not spores) suc- 

 cumb in a dry atmosphere in a comparatively short time, several hours to 

 several days. The spores may, however, survive dryness for many months. 



The dry-air temperature usually employed for germicidal purposes, 

 ranges from 100 C. to 150 C., acting for one hour or longer. A dry heat of 

 145 C. acting for one hour is sufficient to kill all bacteria, including the 

 spores. Temperatures used for purposes of disinfection and sterilization 

 range from 60 C. to 120 C. 60 to 75C. is usually employed in the pasteuri- 

 zation of milk and in sterilizing sera, vaccines, certain culture media (as 

 egg albumen, blood serum), etc. Moist heat of 100 C. in the form of cir- 

 culating steam vapor is much used. To obtain a moist temperature above 

 1 00 C., an autoclave is necessary, or liquids may be employed which boil 

 at a temperature higher than 100 C. as cumene. 



D. Cold. Cold, 10 C. and lower, has decided aseptic properties, that 

 is, it checks bacterial growth and activity very effectually, as has already 

 been explained. Prolonged freezing is, however, necessary to kill bacteria. 

 Cold may therefore be considered a most excellent check upon bacterial 

 activity, but it is a very poor germicide. Cold is a universally recognized 

 and an extensively used food preservative, due to its checking influence 

 upon bacterial growth. 



E. Agitation. The agitation of gases and liquids reduces the bacterial 

 activity therein. Still waters become stagnant but running waters do not, 

 in the comparative sense, due in part to the difference in the oxygen content. 

 Agitating and churning contaminated liquids checks bacterial development 

 somewhat. The active circulation of contaminated air reduces the number 

 of bacteria present. Agitation is, however, not a satisfactory means of 

 sterilization and disinfection. 



F. Sedimentation and Filtration. Sedimentation in sewage waters and 

 other contaminated liquids, combined with nitration, is a very effectual 

 means of purification. Precipitation and filtration, aided by chemicals as 

 alum, iron sulphate, and other coagulants, are much employed in the puri- 

 fication of water supplies. 



G. Free Circulation. Free circulation of air and water are most favor- 

 able to sanitation because of the checking influence upon bacterial activity 

 and also because of the disseminating and diluting effects upon the organisms 



