SCIENTIFIC RESEARCH IN PRACTICE. 253 



can be purified by a similar process, provided the filter is 

 sufficiently dense. 



The theory of the use of antiseptics was scientifically estab- 

 lished as early as 1839, when SCHWANN published his discovery 

 that yeast-cells are killed by the action of certain chemicals, 

 and that fermentation may be brought to a complete standstill 

 by such treatment. 



2. The PASTEUR period dates from 185*7. The great service 

 performed by this investigator was his proof that bacteria 

 exert an influence on different fermentations, and that they 

 can produce diseases in liquids which are undergoing alcoholic 

 fermentation. The necessary practical deductions lead to 

 attempts, for example, to prevent the access of impure air to 

 the liquids. The consequence 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 air in the fermenting rooms. 



The statements in Chapter VII. of PASTEUR'S "Etudes sur 

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

 wort during cooling, should also be alluded to. By means of 

 direct determinations of the amount of oxygen in 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 clarification, but 

 that when the proportion of oxygen in the wort exceeds 

 certain limits it may 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 proved possible 

 to establish any fixed rules for practical guidance. These 

 must be determined by trial experiments for each individual 

 case. 



SCHEELE and APPERT'S method for the treatment of vinegar, 

 wine, and beer, at high temperatures, was taken up by PASTEUP^ 

 and through his great authority obtained a wide application 

 (the so-called Pasteurising). Milk has recently been treated 

 in this manner, more especially since KOCH proved that the 

 tuberculosis bacillus is so widely distributed. 



The experiments on aeration described in " Etudes sur 



