CHANGES ACCOMPANYING BREAKING OF REST PERIOD 23 



The amount of starch solution added to the vial was just suf- 

 ficient to cover the 5 gr. of cortex so that all material had a chance 

 to act, and all starch was exposed to action by the ferments. As 

 soon as the starch was added and mixed with the mass of cortex 

 material, the vials were put in an incubator at a temperature of 

 35 C. 



At intervals of one or two hours, the material in each vial was 

 again thoroly mixed by stirring with a clean glass rod. Later J/2 to 

 1 cc. of the liquid from each sample was removed by means of pi- 

 pettes and placed in a number of Syracuse watch glasses. Two 

 watch glasses were used for each sample. The watch glasses, which 

 had flat bottoms, were placed on a white surface near a good natural 

 light. A few drops of iodine solution were added to the liquid in 

 each glass. Whenever the color produced by the addition of the 

 iodine faded out, more iodine was added until a permanent color 

 was obtained. Care had to be taken not to add too much iodine as 

 this would have obscured the color. 



Iodine added to starch produces a characteristic blue color. 

 If starch has been subjected to the action of a starch-changing fer- 

 ment, such as diastase, for a time, then the addition of iodine no 

 longer produces a blue color, but instead a blue-purple or violet, 

 red-purple, red, red-brown, yellow-brown or no color at all. The 

 particular color obtained depends upon the amount of enzyme which 

 is acting, and upon the time it is allowed to act if temperature and 

 other factors are constant. If a given amount of ferment acts on 

 starch for a short time, then a blue-purple color is obtained by add- 

 ing iodine; if it acts for a very long time, there is no color reaction. 

 If a very small amount of enzyme acts on starch for a given time, 

 there will be a blue-purple reaction with iodine at the end of that 

 time. A much larger quantity of ferment acting on the same amount 

 of starch for the same time may give a red-brown reaction. Since 

 the color obtained with iodine indicates the degree to which starch 

 has been changed, 1 and since the enzymes are responsible for the 

 change, then the color obtained at the end of a definite time will 

 serve as a basis for measuring the enzyme activity. In these experi- 

 ments the colors obtained at each trial were carefully recorded. All 

 determinations were made in duplicate except in a few cases where 

 the material was too scarce. In practically every case the dupli- 

 cates showed the same reaction. 



1. Green, J. Reynolds. The Soluble Ferments and Fermentation. (2nd 

 Ed. Cambridge 1901). 



