MICROSCOPICAL AND PHYSIOLOGICAL EXAMINATION. 21 



bent tube is closed with an asbestos or cotton-wool filter, 

 which is either screwed on or placed over the end (d). 

 For further particulars respecting the treatment of these 

 vessels, see Hansen's " Untersuchungen aus der Praxis der 

 Garungsindustrie." 



6. NUTRITIVE SUBSTRATA. 



With regard to the nutritive substrata, the problem 

 naturally always consists in finding those which are best 

 suited to the respective organisms. If they also possess the 



a 



FIG. 6. 

 Carlsberg Vessel. 



advantage of being per se less favourable for the development 

 of competing forms, it is a great point gained. The rule 

 must of course be borne in mind, when comparative investi- 

 gations are made in different directions, that the nutritive 

 liquid must always remain the same. For the investigation 

 of alcoholic ferments Hansen generally uses hopped wort from 

 the filter-bags ; in special cases of investigations of this kind 

 yeast- water with an addition of glucose, or a solution of cane- 

 sugar or some other sugar, is employed. If it is desired to 

 use a solid nutritive material, the liquid may be mixed with 



