8 APPARATUS 



In the Arnold, sterilization is effected by streaming steam at iooC. 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 everywhere for the sterilization of surgical dressings. 



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

 steam from an adjacent boiler. More recently a method of employing kerosene, gaso- 

 lene, or alcohol with a gravity system has been perfected. During the past ten years, 

 in the laboratory of the U. S. Naval 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 fermen- 

 tation tubes in the autoclave on account of the boiling up of the media and wetting 

 of the plugs. This is still done with the Arnold. By use of the Durham tubes 

 which are to be preferred, except for gas analysis sugar media can be thus sterilized. 



Should a small bubble remain in the top of the small inverted inner tube after 

 removal from the autoclave, one may make a mark with a grease pencil at the line 

 of the bubble; or, if preferred, the basket of Durham tubes can be heated to boiling 

 for ten minutes in a pan of water or in the Arnold when, after cooling, the bubble will 

 be found to have disappeared. 



Glassware will come out from such an autoclave with wrappers as dry and plugs 

 of the test-tubes as stopper-like as could be effected in a hot-air sterilizer. 



The objection which exists in the use of some autoclaves, as regards condensa- 

 tion on dressings or apparatus, does not exist in this type. The mechanism, by 

 which the inner and outer chambers are connected and disconnected, and that for 

 vacuum production, rests in the simple turning of a lever from mark to mark. We 

 have been able with a gas burner to obtain a pressure of 15 pounds in less than ten 

 minutes. In sterilizing test-tubes we place them in small rectangular wire baskets, 

 6X5X4 inches. These baskets are to be preferred to round ones, as they pack more 

 satisfactorily in the refrigerator used for storing media. In sterilizing flasks, test- 

 tubes, Petri dishes, throat swabs, pipettes, etc., it has been our custom, after ex- 

 posing to 20 pounds' pressure for twenty minutes, to produce a vacuum for two or 

 three minutes; then with the steam in the outer jacket for a few minutes to thor- 

 oughly dry the articles in the disinfecting chamber. The valve to the inner chamber 

 is then opened to break the vacuum; the door is now opened, and the articles re- 

 moved in as dry a state as if they had been in the hot-air sterilizer. Articles, how- 

 ever, can be thoroughly dried without the use of a vacuum, simply allowing the steam 

 to remain in the outer jacket with the steam cut off from the inner chamber. 



