EXAMINATION OF AIR AND WATEE. 51 



tance for the brewery, but only for the malt-house. By way of 

 a closer approximation to practical requirements, HANSEN pro- 

 poses the following method of procedure. The flasks containing 

 a development of yeasts and bacteria are divided into two 

 groups : (1) those in which the growths soon appeared, and 

 (2) the remainder, in which they made their appearance later ; 

 as, for instance, after five days. Among the latter growths are 

 those species which develop less readily in wort ; and in the 

 brewery these will therefore be generally suppressed by the 

 yeast, and are consequently of less importance in the examina- 

 tion of water or air. Analyses according to this method have 

 been executed by HOLM, WICHMANN, and several others, and 

 the method has always been used in the author's laboratory. 



For the control of air and water filters KOCH'S gelatine 

 method can be advantageously used. 



