152 Dr. W. Roberts. Estimation of the Amy loly tic [May 5, 



of each testing was noted. When the achromic point was reached the 

 time was marked, and the interval from the commencement of the 

 experiment was computed. If at the end of three minutes the 

 mixture still gave the blue reaction of unaltered starch, a new experi- 

 ment was made, using two, three, or four times the quantity of extract. 

 If, on the other hand, the achromic point was reached in less than two 

 minutes, a new experiment was made, using a smaller quantity of 

 the extract. Two or three experiments generally sufficed to determine 

 the quantity of extract required to bring the achromic point within a 

 period ranging from two to ten minutes. A final control experiment 

 enabled the operator to fix the achromic point somewhere between 

 four and six minutes. The accuracy of the method depends chiefly on 

 the sharpness and precision with which the occurrence of the achromic 

 point can be determined. If it occur earlier than two minutes, the 

 transition is too rapid for exact observation and record. On the other 

 hand, if it occur later than fifteen or twenty minutes the transition is 

 too gradual for precise limitation. The most satisfactory results are 

 obtained when the achromic point falls between four and six minutes. 



The following example will serve as an illustration of the way in 

 which the experiments were carried out, noted, and expressed : — 



Table IY. 



10 cub. centims. standard starch mucilage + 90 cub. centims. water 

 + 0'1 cub. centim. pancreatic extract — at 40° C. 



Time. Reaction with iodine. 



10.30 A.M Commencement of experiment. 



10.31 „ Blue. 



10.32 „ Violet. 



10.33 „ Brown. 



10.34 ,, Yellowish-brown. 



10.35 „ Pale yellow. 



10.36 ,, No reaction — achromic point. 



6 minutes. 



Achromic point reached in 6 minutes. 



The result of the experiment was expressed in the first instance as 

 follows : 0*1 cub. centim. pancreatic extract + 10 cub. centims. standard 

 mucilage = 6 minutes at 40° C. 



From this somewhat incongruous expression it is however easy to 

 extract by a simple formula a correct and convenient expression 

 for the diastasic value of any amylolytic solution. 



Mode' of Calculating and Expressing the Diastasic Value. 

 The principle of the method consists, as already stated, in ascertaining 



