EXPERIMENT STATION BULLETINS 



231 



Dry heat can be made very effectual by using a higli degree, which for a 

 short time will accomplish more than could be expected of steam. .Instead 

 of using the discontinuous heating plan, one sterilization will be sufficient. 

 Dry heat is usually applied in two ways, the direct flame and the 



oven. 

 Flame. Wherever the flame may be utilized as an agent to kill bacteria, 



no more positive and satisfactory means could be offered. Its 

 uses are, however, very limited. In the laboratory, the platinum needle 

 which is used for inoculation is brought to a red hent and is thus sterilized. 

 Old knives and scissors employed for post-mortem work are rendered free 

 from life. This intimates the possible uses. On the farm old knives and 

 instruments used in the cutting of animals dead from anthrax, blackleg, 

 tuberculosis, or any infectious diseases are safe only after they have 

 emerged from the purifying influence of the flame. In this connection, 

 although it does not properly belong under this head, may well be added 

 that the disposal of carcasses in which infection was present or suspected 

 or in fact the disposal of any material which would be likely to convey 



danger is by far the best accomplished through the flame. 

 Hot air oven. j^ ^j-y j^eat sterilization, 



the hot air oven has wide 

 application and as a practical sterilizer 

 is of great importance. It is a simple 

 double walled oven, having|an air space 

 between the walls which opens near and 

 about the flame; otherwise it closely 

 resembles the oven of a gasoline stove. 

 In the top are holes for the thermom- 

 eter and tbermo-regulator which regu- 

 lates the supply of gas and heat. 

 (This instrument will be described 

 with the incubator. ) 



The hot air oven is designed for the 

 sterilization of glassware and other 

 hard and dry materials not injured by 

 an exposiire to a high degree of dry 

 heat. Clothing can be sterilized but 

 with more difficulty than articles whose 

 surfaces are exposed. Instruments 

 may be made bacteriologically clean in ^^^- ^*' ^°^ ^^^ °'^®°' 



this manner; attention must be given to the degree of heat, lest the temper 

 which is of so much value in some instruments be destroyed. 

 ■ It has been found that 128° C. [262° F. ] will kill the vegetative forms and 

 that 140° O. [284° F.] is required to destroy the spores; consequently it is 

 customary to heat the oven to 150° C. [302 F.l for one hour to insure 



absolute sterilization. 

 Chemicaia. Chemicals are mostly used as disinfectants, and are not 



regarded with much favor as sterilizers. There are several 

 reasons for this. It would be absurd to sterilize or attempt to sterilize 

 media with a chemical which acts as a germicide — germ killing — and which 

 generally is actively poisonous. It would be substituting for bacteria a 

 poison as detrimental as the bacteria themselves. Agents of this kind 

 seldom kill outright, or within several hours, but rather retard develop- 



