METHODS OF STERILIZATION 11 



SIMPLE STEAM STERILIZER 'NOVY/ 



The lower part of the apparatus consists of an ordinary water 

 bath, 7 to 8 inches in diameter ; the upper part of a copper pail 

 8 inches high and 8 inches in diameter, with a perforated bottom, 

 and lid with a tube ; copper rings are soldered in the interior of the 

 pail to prevent the tube touching the sides, otherwise the cotton 

 plugs would become saturated with the condensed steam. The pail is 

 filled with flasks or tubes, and placed over the water bath, in which 

 the water should be boiling. In five to seven minutes steam will 

 actively issue from the tube in the cover, showing that the interior 

 temperature has reached 100 C. With the apparatus a student can 

 attend to any needed steam sterilization at his own table, and thus save 

 much time. The general usefulness of the apparatus, its compactness, 

 cheapness, and the saving in the gas, will recommend it to those 

 practitioners who desire to equip a small laboratory. 



A small steam sterilizer may be readily improvised by standing an 

 inverted funnel of appropriate size upon the water bath. If the 

 funnel is of glass it is well to surround it w r ith a towel, to prevent its 

 cooling too rapidly on removal. Dr Nuttall states that he has used 

 this simple apparatus frequently during the last ten years and found 

 it very useful. 



TYNDALUS DISCONTINUOUS METHOD OF 

 STERILIZATION. 



We have stated above that certain bacteria form spores which are 

 highly resistant, whereas the vegetative form of the organism is more 

 sensitive to heat, chemical agents, etc. TyndalPs method of discon- 

 tinuous sterilization depends upon the principle that bacteria develop- 

 ing from spores in the nutrient media are destroyed by a relatively 

 short exposure to a temperature of 100 C., at which temperature 

 the spores are not affected. To overcome this difficulty presented by 

 the resistance of the spores, the tubes of media or other materials are 

 placed in a steam sterilizer at 100 C. for thirty minutes. The first 

 heating not having killed the spores, the material is placed at ordinary 

 room temperature, or better, at 37 C., when any living spores quickly 

 vegetate. The bacteria to which the spores give birth are killed by a 

 second heating, for twenty or thirty minutes, on the following day. 

 The above operation repeated three, four, or five times, ends in the 

 certain sterilization of the media, all the spores having developed into 

 bacilli, and as such destroyed. 



