76 PRACTICAL PHYSIOLOGY 



(B) ON FLUID. (a) Disappearance of Sugar. (Demonstration.) 

 The original solution (A) and the solution after incubation (B) 

 have been boiled for some time with phenylhydrazine and acetic 

 acid, which forms a yellow insoluble compound with glucose. Note 

 the difference in the amounts in (A) and (B). 



(b) Formation of Alcohol. Some of the fluid from tubes 1, after 

 being in the incubator, is distilled. To about half an inch of the 

 distillate, add a few drops of potassium bichromate and a little 

 dilute sulphuric acid and warm. Note : 



1. Pungent odour Aldehyde. 



2. Green colour. 



(c) Nature of Gas evolved. (Demonstration.) With a fine pipette 

 add KHO dissolved in alcohol to a Doremus' ureometer in which 

 the solution has been incubated with yeast, and note the absorption 

 of the gas evolved CO 2 . 



4. CONCLUSIONS. (1) What has happened to the yeast in each 

 of the tubes ? 



(2) What conclusions do you come to as to the influence upon 

 the yeast protoplasm of the various conditions to which it has been 

 subjected ? 



(3) How has the growth of the yeast taken place ? 



(a) Where does yeast protoplasm get material for growth ? 

 (6) Where does yeast protoplasm get energy for growth ? 1 



1 For Enzyme Action, see Chemical Section. 



