284 PHYSIOLOGY OF NUTRITION. 



taining water and broken ice. If an experiment is to be inter- 

 rupted before the fermentation is completed, in order, e.g., to de- 

 termine the quantity of alcohol produced at the end of a definite 

 time, we open the fermentation vessel and add to the food solu- 

 tion 20 c.c. of 5 per cent, corrosive sublimate solution, so as to 

 secure instantaneous cessation of the fermentation. 



The apparatus here described is very serviceable, e.g., when it is 

 required to prove that yeast brings about vigorous fermentation in 

 wort, both in absence of Oxygen and in presence of air, while 

 with Pasteur's food solution the fermentation is only feeble in 

 presence of air, but active in absence of Oxygen. Regarding the 

 yeast to be employed, consult the appendix. To the food solution 

 in A must be added a few c.c. of yeast fluid. 1 



If it is only desired to prove qualitatively that alcohol is formed 

 during fermentation, we proceed in exactly the same way. The 

 distillate obtained is, however, again subjected to distillation. The 

 fluid now obtained smells strongly of alcohol; it is inflammable. 

 If we dissolve some Potassium bichromate in a little water, add to 

 it some concentrated Sulphuric acid, and introduce a few drops of 

 the mixture into the last distillate, it becomes green, because the 

 Chromic acid is reduced, the alcohol present being oxidised. 



To prove the very important fact that the higher plants in 

 absence of free Oxygen, while they undergo intramolecular respi- 

 ration and at last gradually perish, produce alcohol, we experi- 

 ment with grapes, cherries, or peas. The objects are laid for a 

 minute in corrosive sublimate solution (I: 1 1,000), so as to kill any 

 yeast-cells which may be clinging' to them externally, and then 

 well rinsed with w r ater. The fruits are now at once used for the 

 investigation, while the pea seeds are soaked in water, and ger- 

 minated for one to two days on moist blotting-paper.* We now 

 quite fill a litre flask with the fruits or seedlings and close it with 

 a rubber stopper through which passes the shorter limb of a glass 

 tube bent twice at right angles. The longer limb of this tube 

 dips into mercury. The Oxygen in the apparatus is soon con- 

 sumed. Intramolecular respiration speedily sets in, which results 

 in an evolution of gas continuing often for weeks, but ultimately 

 becoming slow, and at last completely ceasing, when the objects 

 are dead. If in this state brought into the air, they rapidly 

 undergo decomposition. When the fruits or seedlings have been 



* The water and blotting-paper must first of all be sterilised. 



