48 MICRO-ORGANISMS AND FERMENTATION. 



know whether the water and the air contain such germs as 

 are capable of developing in wort and beer. This cannot, 

 as was formerly assumed, be ascertained by means of the 

 meat-decoction peptone gelatine employed in hygienic air- 

 and water-analysis. The zymotechnologist has this great 

 advantage over the hygienist, that he is in a position to make 

 direct experiments with the same kind of liquid as that 

 employed in practice, namely wort. All disease germs that 

 have hitherto been shown with certainty to occur in beer are 

 also capable of developing in wort. Hansen's comparative 

 investigations have proved beyond dispute that the use of 

 gelatines introduces great sources of error. Thus, for 

 instance, in a series of comparative experiments with corres- 

 ponding samples of water, the following numbers were 

 obtained: In Koch's nutritive gelatine: 100, 222, 1000, 

 750, and 1,500 growths were obtained from 1 ccm. of water ; 

 in wort 0, 0, 6*6, 3. and 9 growths ; whereas, in beer, none of 

 these water-samples gave any growth. In another series, 

 Koch's gelatine gave for 1 ccm. of water 222 growths, wort- 

 gelatine 30 ; but none of the flasks containing wort and beer, 

 and infected with the water, showed any development of 

 organisms. Thus, only very few, or none at all, of the great 

 number of living germs in the water developed in wort or 

 beer. 



Hansen has further shown, that in zymotechnical analyses 

 of water and air, it is a mistake to employ gelatine at the 

 outset, and then to transfer the colonies that have been 

 formed into wort-flasks. Thus, he demonstrated by experi- 

 ments that several of the bacterial germs existing in atmo- 

 spheric dust and in water are capable of developing in 

 nutritive gelatine, but not in wort; but several of these 

 species become invigorated to such a degree after having 

 formed a new growth in the gelatine, that they are then 

 enabled to develop in the less favourable medium, wort. 

 In such cases the experimenter is therefore deceived. 

 Another, and a still greater, objection to the gelatine 



