STERILIZATION OF MILK. 



149 



rials have been used for filter for the purpose of steri- 

 lizing fluids. Zahn used burnt clay, as did also Tiegel and 

 Klebs. Gypsum was used by Pasteur and others, porce- 

 lain by Chamberland, fayence by Gautier, and asbestos 

 cardboard and plastic charcoal by Hesse and Breyer. All 

 these substances easily take up the mechanical materials 

 suspended in a fluid, and thus also the bacteria, on the re- 

 moval of which the fluid will keep. 



As Zahn's experiments in my opinion in a very simple 

 and plain manner illustrate the preservation of milk by 

 filtration, I shall briefly describe his method of procedure. 

 Into a porcelain tube glazed on the outside he fitted tightly 

 a rubber stopper, in which a tube connected with an aspi- 

 rator was placed. The apparatus was then sterilized. 

 When cold, it was lowered into the milk 

 and the aspirator opened. By means of 

 this simple apparatus, shown in the accom- 

 panying illustration, Zahn succeeded in 

 sterilizing the milk. (Fig. 25). 



Several different kinds of apparatus for 

 sterilizing fluids by filtration are made at 

 the present time; none of these are fully 

 practical, however; the most promising 

 ones are the porcelain filters of Chamber- 

 land's mentioned in the preceding, which 

 act continuously and regularly. 



It is easy to sterilize milk in this manner, but unfortu- 

 nately it is changed also in other ways by this method. 

 Duclaux has thus shown through lengthy experiments 

 that not less than nine tenths of the albumen content 

 of the milk remains in the filter. The albuminoids are 

 not really dissolved in the milk, but appear in it in an 



FIG. 25. 



