40 MICRO-ORGANISMS AND FERMENTATION'. 



of 10 litres, are made of tinned copper, are cylindrical in shape, 

 and conical at the top ; at the apex of the cone a twice-bent 

 tube (c d) with or without an enlargement (e) is either soldered 

 into or screwed into the flask. At one side of the cone is the 

 inoculating tube and glass stopper (a), and near the bottom of 

 the vessel is another tube (6) for drawing off the fermented 

 liquid and the yeast. This tube is provided with a pinch- 

 cock. When the liquid is sterilised, the bent tube is closed 

 with an asbestos or cotton-wool filter, which is tightly packed 

 on to the end (d). 



In the new model (Fig. 11) the bent tube is ground into the 

 upper part of the flask, and fastened by means of a screw, 

 allowing the whole of this part to be detached, when the flask 

 is to be cleaned ; the filter is screwed into the end of the bent 

 tube. 



t 6. Nutritive Substrata. 



With regard to the nutritive substrata, the problem 

 naturally consists in finding those which are best suited to 

 the respective organisms. If they also possess the advantage 

 of being less favourable for the development of competing 

 forms, it is a great point gained. The fact must, of course, 

 be borne in mind, when comparative investigations are made 

 in different directions, that the nutritive liquid must always 

 remain the same. 



For the investigation of yeasts, hopped - beer wort forms 

 the best nutrient. It is best taken from the filter-bags, 

 because these yield a smaller deposit on boiling in the flasks. 

 It is also suitable for many bacteria and moulds, but for 

 certain bacteria (e.g., lactic acid bacteria) the sweet wort, 

 without hops, is used, and this is also adapted for use with 

 moulds. Amongst the artificial nutritive fluids for yeast, 

 Pasteur's (1860) has an historical interest. The renowned 

 scientist used this to upset Liebig's theory with regard to the 

 indispensability of albuminoids for fermentation. It consists of 

 100 c.c. of water, 0-075 gramme of the ash of yeast, 10 grammes 

 of sugar, and 1 gramme of ammonium tartrate. A good 

 nutritive fluid can also be prepared from yeast decoction with 



