i 4 o PLANT PHYSIOLOGY 



If the student's course up to this point has been such as to 

 inspire him with the genuine scientific spirit, he will be unwill- 

 ing to leave this subject of fermentation until he has made his 

 study of it quantitative, and he will wish to determine whether 

 the carbon dioxide and alcohol formed equal the sugar used. 

 An exact determination of this, especially for the alcohol, pre- 

 sents great difficulties, but for the carbon dioxide they are not 

 insuperable, as may be found by use of the following: 



Suggested Experiment. Prepare the apparatus of figure 36, but with- 

 out the thermometer and with mercury in place of water. Place in the 

 flask one gram of grape-sugar with the suitable quantities of minerals, water, 

 and yeast, and give favorable conditions for fermentation. Collect and 

 measure the evolved gas, taking the carbon dioxide present in the flask at 

 the close of the experiment to balance the air present at the beginning. Then 

 using the equation C 6 H 12 O r , = 2C 2 H 6 + 2C0 2 , determine the relation be- 

 tween the grape-sugar used and the carbon dioxide formed. Some error 

 must be allowed for formation of a small percentage of other substances. 

 The disappearance of the sugar may be tested by use of Fehling's solution. 



The student should now extend his knowledge through the 

 literature to include our present information upon the energy 

 relations of fermentation, the participation of enzymes therein, 

 other forms of fermentation and their relations to enzymes, and 

 the significance of the process to the organisms concerned. Nor 

 should he leave the subject without a clear knowledge of the 

 leading facts in the economics of the process. And he should 

 also make himself acquainted with the homologous processes 

 involved in decay. 



The student is now prepared to understand, and should 

 make sure of his knowledge of the interrelationships of aerobic 

 and anaerobic respiration and fermentation, the chemical stages 

 or steps therein, and the evidence as to whether respiration is at 

 the expense of the living protoplasm itself, or of carbohydrates 

 or other substances saturating the protoplasm. Upon these im- 

 portant matters he will find the paper by Barnes cited below 

 especially valuable. And, as always, he should express his 

 arranged knowledge in a forcible exposition. 



Respiration, with its need for access of oxygen and for removal 

 of carbon dioxide, becomes the center of some important eco- 



