APPARATUS FOR STERILIZATMN. 5 



in which a temperature of about 150 C. is maintained for one hour, is 

 ordinarily used for the sterilization of Petri dishes, test-tubes, pipettes, 

 etc. If the temperature is allowed to go too high, there is danger of 

 charring the cotton plugs and also of causing the development of an 

 empyreumatic oil which makes the plugs unsightly and causes them to 

 stick to the glass. Again we must be careful not to open the door until 

 the temperature has fallen to 60 C., otherwise here is danger of 

 cracking the glassware. Where gas is not obtainable, the hot-air 

 sterilizer is not a very satisfactory apparatus. 



The Arnold sterilizer is to be found everywhere and can be used on 

 blue-flame kerosene-oil stoves as readily as with gas burners. The 

 most convenient form, but more expensive, is the Boston Board of 

 Health pattern. The ordinary pattern, with a telescoping outer 

 portion, answers all purposes, however. In the Arnold, sterilization is 

 effected by streaming steam at 100 C. It is usual to maintain this 

 temperature for fifteen to twenty-five minutes each day for three suc- 

 cessive days. The success of this procedure fractional sterilization 

 is due to the fact that many spores which were not killed at the first 

 steaming have developed into vegetative forms within twenty-four 

 hours, and when the steam is then applied such forms are destroyed. 

 Experience has shown that all the spores have developed by the time of 

 the third steaming, so that with this final application of heat we secure 

 perfect sterilization. 



It is customary to use the Arnold for sterilizing gelatin and milk 

 media, even when the autoclave is at hand, the idea being that the 

 greater heat of the autoclave may interfere with the quality of such 

 media. The most convenient autoclave is the horizontal type, such as 

 is to be found even-where for the sterilization of surgical dressings. 

 The source of heat may be either gas, the Primus kerosene-oil lamp or 

 steam from an adjacent boiler. During the past year, in the labora- 

 tory of the U. S. Xaval Medical School, we have been using a dressing 

 sterilizer, made by the American Sterilizer Co., with which it has been 

 possible to most satisfactorily carry out all kinds of sterilization thus 

 doing away with the use of the Arnold and the hot-air sterilizer. It 

 is impossible to sterilize ordinary fermentation tubes in the autoclave 

 on account of the boiling up of the media and wetting of the plugs. 



