MEANS OF STERILISATION 



23 



Aerobiosis. — Pasteur was the first to lay emphasis upon the 

 effect which free air had upon micro-organisms. He classified them 

 according to whether they grew in air, aerobic, or whether they 

 flourished most without it, anaerobic. Some have the faculty of 

 growing with or without the presence of oxygen, and are designated 

 as facultative aerobes or anaerobes. As regards the cultivation of 

 anaerobic germs, it is only necessary to say that hydrogen, nitrogen, 

 or carbonic acid gas may be used in place of oxygen, or they may 



Fig. 7.— Method of producing Hydrogen by Kipp's Apparatus for Cultivation of 

 Anaerobes (see p. 117. 



be grown in a medium containing some substance which will absorb 

 the oxygen (see p. 117). 



Means of Sterilisation. — As this term occurs frequently even 

 in books of an elementary nature, and as it is expressive of an idea 

 which must always be present to the mind of the bacteriologist, it 

 may be desirable to make allusion to it here. 



Chemical substances, perfect filtration, and heat are the three 

 means at our command in Order to secure germ-free conditions of 

 apparatus or medium. The first two, though theoretically admissible, 

 are practically seldom used, the former of the two because the 

 addition of chemical substances annuls or modifies the operation, 

 the latter of the two on account of the great practical difficulties in 

 securing efficiency. Hence in the investigations involved in 

 bacteriological research heat is the common sterilising agent. A 

 sustained temperature of 70° C. (158° F.) will kill all bacilli; even 

 58° C. will kill most kinds. Boiling at 100° C. (212° F.) for five 

 minutes will kill anthrax spores, and for thirty to sixty minutes 

 will kill all bacilli and their spores. This difference in the thermal 



