Ii8 



Scientific Proceedings (38). 



which is accepted as being characteristic of starch. (Claude Ber- 

 nard found a form of glycogen in paralyzed muscles which gave a 

 blue reaction with iodine.) The blue coloration is proportional to 

 but more intense than the corresponding violet previously ob- 

 tained, so that even when the violet coloration was scarcely dis- 

 cernible a good blue reaction was observed. The optimal 

 temperature of the starch-dextrin reaction is distinctly higher than 

 the temperature at which the reversion occurs, but the exact point 

 has not been determined. The occurrence of the reversion at the 

 optimal temperature of saccharification is doubtless merely a coin- 

 cidence. 



2. When digestion has proceeded to the point at which there 

 is not a color reaction with iodine, in other words to the achroo- 

 dextrin-su gar stage, heating the preparation as above did not cause 

 either a starch-dextrin or an erythrodextrin-achroodextrin rever- 

 sion, as was shown by the continued absence of any color reaction 

 with iodine. 



3. By testing the preparations before and after heating with the 

 usual copper-reducing tests, and with the polariscope, both dextrin- 

 maltose and maltose-glucose reversions were occasionally detected, 

 but the results were very inconstant and generally not absolutely 

 conclusive. The absence of a constant occurrence of these rever- 

 sions is doubtless owing to a failure to obtain the exact concentra- 

 tion of solution in relation to temperature. 



4. The starch-dextrin reversion is not permanent unless the 

 preparation has been heated to the temperature at which the enzyme 

 is destroyed. Upon cooling a preparation that has been heated to 

 only a lower level a reconversion of the starch into dextrin occurs, 

 with of course a loss of the blue reaction and a return of the vio- 

 let reaction with iodine. 



5. The starch-dextrin reversion is not enzymic, but dynamic, 

 and, therefore, the mechanism is quite different from that of the 

 reversions recorded by previous observers. Formaldehyde in even 

 small amounts is, as is well known, highly destructive to amylase, 

 and when added to the starch-dextrin solution absolutely prevents 

 the reversion. This might be taken as showing that the absence 

 of reversion is due to the destruction of the enzyme, but this is 

 negatived by the fact that the addition of strong mineral acids in 



