RESULTS OF SCIENTIFIC RESEARCH IN PRACTICE. 205 



filter (Schroder and Dusch). From this, the result was also 

 arrived at that water can be purified by a similar process, 

 provided the filter is sufficiently dense. 



2. The Pasteur period dates from 1857. The great 

 merit of this investigator was that he proved that bacteria 

 exert a disturbing influence in different fermentations, and 

 that they can produce diseases in liquids which are under- 

 going alcoholic fermentation. 



It is therefore necessary to proceed in such a manner that 

 infection of this nature is avoided, and this is best attained 

 by preventing the access of impure air to the liquids. The 

 consequence of this doctrine as regards the brewery is the 

 abandonment of open coolers and refrigerators, the aeration 

 of the wort by air which has been previously sterilised, and 

 the purification of the air in the fermen ting-rooms. 



The statements in Chapter VII. of Pasteur's " Etudes sur 

 la biere " (1876), regarding the importance of the oxidation of 

 the wort during cooling, are also of practical value. By means 

 of direct determinations of the amount of oxygen in the wort, 

 Pasteur showed that a certain quantity of oxygen, partly in 

 the free state, and partly combined in the wort, exerts an 

 influence on the course of the fermentation and on the 

 brightening, but that when the proportion of oxygen in the 

 wort exceeds certain limits it can act injuriously on the 

 character (force et arome) of the beer (page 377). 



Although several investigators have undertaken elaborate 

 researches in this direction, it has not hitherto been possible 

 to establish any fixed rules for practical guidance. These 

 must be determined by trial experiments for each individual 

 case. 



Scheele's and Appert's method for the treatment of vinegar, 

 wine, and beer, at elevated temperatures, was taken up by 

 Pasteur, and through his great authority obtained a wide 

 application (the so-called Pasteurising). Kecently milk has 

 also been treated in this manner, especially since Koch proved 

 that the tuberculosis bacillus is so widely distributed. 



