194 



DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



Table 28. 



They state that the last fi^'e starches were obviously impure, and that they did not 

 yield homogeneous pastes. Successive purifications lowered the angle in each case. The 

 chestnut starch contained evident traces of something other than starch. 



In another series of experiments they used precipitated diastase in the proportion 

 of 0.2 gram per 5 grams of starch at 60 for 1 hour, with the results shown in table 28. 



In another series, with 0.4 gram of precipitated 

 diastase to 5 grams of starch for 2 hours at 60, they 

 recorded the results shown in table 29. 



In an earlier investigation. Ford showed that 

 metallic and other impurities influence amylolytic 

 activity, and that dried starch readily absorbs sub- 

 stances which may interfere with hydrolysis. Ford 

 and Gutlirie state that the contracUctory results of 

 O'Sullivan and themselves are to be attributed to 

 impurity of the potato starch used by 0'Sulli\'an. 

 A specimen of this starch was obtained from O'Sul- 

 livan, and was found to contain copper to the extent 

 of 0.035 per cent. They determined experimentally 

 that this amount of copper is sufficient to bring 

 about a marked reduction in maltose formation. It 

 seems, therefore, cjuite clear from the results of the 

 investigations of both Ford, and Ford and Guthrie, 

 that the source of starch is without influence on the 

 products of decomposition if the starches are suffi- 

 ciently purified and freed from substances which influence amylolytic action. 



That all boiled starches, whatever the source, yield the same decomposition products, 

 quantitatively and qualitatively, under the same conditions of experiment, has been shown 

 by the author's work. To obtain uniform results it is essential to secure as nearly as pos- 

 sible the same conditions of experiment. It seems to be a universally accepted belief that 

 enzymes in a 1 to 2 per cent solution of chloroform, or in other antiseptic solutions which are 

 inert towards the enzyme, do not undergo rapid impairment in energy. While this is in a 

 large measure justified in regard to plant enzymes, such is not the case with amylopsin and 

 ptyalin and probably all animal enzymes. Even within 24 hours such diastatic enzymes 

 show deterioration, which steadily increases with time. Therefore, in making compar- 

 ative experiments the solution of enzyme should be made immediately before using. It 

 is also of importance that none of the starch be lost after boiling, by adherence to the sides 

 of the vessel, and that other specific standard conditions be maintained. A large number 

 of experiments were carried out with Merck's "pure ptyalin," "pure pancreatin," and 

 "medicinal malt diastase," and also with Parke, Davis & Company's Taka-diastase. 

 These enzymes showed marked differences in energy, Taka-diastase being the most ener- 

 getic, pancreatin a shade less energetic, malt diastase distinctly less energetic than the 

 foregoing, and ptyalin comparatively weak. It is, therefore, manifest that, in making 

 comparative studies of different starches, a given enzyme must be used throughout. More- 

 over, as the different preparations of the same enzyme differ widely in energy and also in 

 their content of glucase, etc., the same preparation must be used throughout for control 

 experiments made to permit of proper corrections. 



A number of experiments were made with starches prepared from Solanum tuherosum, 

 Zea mays, Batatas edulis, Canna roscoeana, Canna loarszewiczii, Canna musa^folia, Canna 

 edulis, Maranta arundinacea, Freesia refracta var. alba, Dieffenbachia seguine, and other 

 starches derived from widely separated genera, orders, etc. In each experiment 0.5 gram 

 of starch was boiled in 35 c.c. of water for 1 minute, the preparation cooled, the starch 



