58 



PHYSIOLOGY OF NUTRITION 



by water vapor at ioo°C. The apparatus is covered with felt or asbestos, to 

 retard the escape of heat. d 



Instead of a steam sterilizer the autoclave is frequently used for steriliza- 

 tion (Fig. 35). This is nothing more than a Papin's digester, operating with 

 superheated steam, under pressure up to two atmospheres or more and at 

 temperatures of from ioo° to i34°C. or higher. At a temperature of i2o°C. 

 sterilization need last only fifteen minutes. At a temperature of 130 all 

 germs are instantly killed, so that repeated treatment, necessary in the case 

 of steam sterilization, is here superfluous. 



Fig. 34. — Arnold steam sterilizer. 



Liquids may also be sterilized by filtration. The most convenient arrange- 

 ment for this purpose is the Chamberland filter, a hollow cylinder of porous 

 porcelain, closed at one end. The liquid to be sterilized is passed, under pres- 

 sure, through the porous walls of the previously sterilized filter. 



Various disinfecting materials are also used for the chemical destruction of 

 microorganisms. The most effective of these is corrosive sublimate, or mercuric 

 chloride (HgCl 2 ). A solution of 1 g. of mercuric chloride in a liter of distilled 

 water is thus used in bacteriological laboratories. The hands of the worker and 

 also his implements are disinfected with this solution, which is also employed to 

 destroy cultures that are not needed. A solution of one part of the salt in 

 300,000 parts of water prevents the development of the bacillus of splenic fever, 



d One of the various forms of the Arnold type of steam sterilizer is very convenient and 

 efficient in operation. (Fig. 34.) This keeps but a small amount of water boiling at any 

 time and a large portion of the water that is boiled away is condensed and returned to the 

 reservoir. — Ed. 



