IQ2 COMPOSITION OF THE DIGESTIVE JUICES. [CH. VIII. 



240. Determine the effect of change of reaction on the chromic 

 period. It will be found that it is least at PH= 6-7, lengthening 

 out as the solution is made acid or alkaline to this. With small 

 changes of reaction, however, the activity is but slightly affected. 

 Determine the chromic period at P H = 5-7 and 7-7. 



241. Wohlgemuth's method. Number a series of clean dry 

 test-tubes i to 10. 



Into i and 2 measure I cc. of the diluted enzyme. 



Into 2 to 10 measure i cc. of distilled water. 



Mix the contents of 2 and transfer i cc. from 2 to 3. 



Mix the contents of 3 and transfer i cc. from 3 to 4. 



Continue in this way, rejecting i cc. of the fluid from 10. 



To each tube add 5 cc. of i per cent, soluble starch (see Note 2), 

 commencing with tube 10. Mix the contents of the tubes and 

 place them in a water bath at 40 C., noting the time when they are 

 placed in the bath. Allow the tubes to remain in the bath for 

 exactly 30 mins. Remove the tubes and immerse them all in cold 

 water to stop the action. 



Arrange them in order in a rack. 



To each tube add cold distilled water to about 2 finger-breadths 

 from the top of the tube. Now add 3 drops of 0-02 N. iodine to 

 each tube and mix, commencing with the tube i. This will probably 

 give no colour, whilst tube 10 will probably give a deep blue. Be- 

 tween these limits tubes will probably be found which are red and 

 purple. Select the tube with the lowest number that has a blue 

 tinge mixed with the red. In the tube numbered one below this 

 there has been enough enzyme to completely convert 5 cc. of soluble 

 starch to erythrodextrin in 30 minutes. 



Wohlgemuth indicates the concentration of enzyme in the 

 following way. He determines the volume of i per cent, starch that 

 would be converted to erythrodextrin by i cc. of the enzyme 

 solution in 30 minutes. He calls this the " diastatic power " of the 

 solution, and indicates it by D for i per cent, and by d for o-i per 

 cent, starch. He also indicates the temperature and period of 

 digestion. Thus in the above experiment, if the 6th tube were 

 blue-violet and the 5th tube were red, then since the 5th tube con- 

 tains iV cc. of the enzyme, and this amount has converted 5 cc. 



