282 PHYSIOLOGY OF NUTRITION. 



boiled out and then allowed to cool thoroughly in closed vessels. 

 In each vessel we now place a few soaked wheat grains, dip the 

 mouths of the vessels under mercury, and replace the water in a 

 by N 2 O, that in b by atmospheric air. In the course of a few 

 days the grains in b germinate ; those in a do not germinate. 

 If, however, they are placed in the air, and exposed to normal 

 conditions of germination, they subsequently develop, if they have 

 not been kept in the Nitrous oxide too long, e.g. for only two 

 days. 



1 See Detmer, Landwirthschl. Jahrbiicher, Bd. 11, p. 218. See also MSller, 

 Ber. d. Deutschen botan. Gesellsch., Bd. 2. 



108. Formation of Alcohol in Plants, and the Behaviour of 

 Anaerobic Organisms. 



We procure some wort from a brewery, transfer say 200 c.c. of 

 it to a flask, and add a small quantity of very pure yeast which 

 lias been made into a pulp with water. The dry weight of the 

 yeast we determine by a control experiment. After some time, 

 when the fermentation, which quickly becomes energetic, has 

 slackened, we collect the yeast in the flask on a weighed filter, and 

 find by determination of its dry weight that a considerable pro- 

 duction of yeast has taken place under the conditions described. 



Saccharomyces cerevisise grows actively if well supplied with 

 Oxygen. But under these conditions, as also with a limited 

 supply of air or complete deprivation of Oxygen, the fungus is 

 ;ible to provoke in certain food solutions very vigorous alcoholic 

 fermentation, as is readily proved by aspirating air through wort 

 to which a fair quantity of yeast has been added, or even by lead- 

 ing Oxygen into it from a gasometer. 



In this and in many other cases it is of importance to obtain 

 a measure of the rate of fermentation. This is secured by deter- 

 mining the quantity of sugar decomposed in the fermentation, or 

 the quantity of alcohol produced. 



In the sugar determinations, 10 c.c. of the Pasteur's solution, 

 for example, with which we experimented, is diluted till the pro- 

 portion of sugar is reduced to J-| per cent., and if cane-sugar has 

 been used for making the Pasteur's solution, is heated for some 

 time with Sulphuric acid. (See above under sugar determination.) 

 The determinations of sugar are then easily made by means of 



