CHAPTER VI. 



METHODS USED IN THE STUDY OF STARCHES IN THIS RESEARCH. 



From the data of the preceding chapters it is obvious that quite a number of very 

 different types of methods and very different substances may be used to demonstrate 

 not only the general properties of starch, but also to differentiate starches from different 

 sources, different grains of the same kind of starch, and different parts of the same grain. 

 Various conditions, such as the limitations of actual needs, of time and assistance, of 

 the number of pages that could with reason be devoted to the report, of expense, etc., 

 have of necessity restricted the number of methods and reagents that could possibly be 

 used to advantage in a field of investigation which involved the study of over 300 

 starches. Hence, it was necessary to select only such as gave promise of positive results 

 and which differ in certain essential respects; hence, optical, physico-chemical, chemical, 

 and photographic methods were chosen, and also such reagents as upon chemical grounds 

 might be assumed to act differently. 



There seems to be no doubt that starches of different origin can to some extent be 

 differentiated from one another by careful analyses of the various proximate coiistituents, 

 both by the inorganic and organic constituents generally; and also by the characters of the 

 starch-substance, which undoubtedly is not a uniform body. Such analytic work was 

 out of question because of the enormous amount of time involved and of the necessarily 

 very limited quantities of starch that could be expected from nearly all of om* sources of 

 supply, unless at very heavy and unreasonable expenditure. Many differences peculiar 

 to genera or species could undoubtedly be brought out by such ordinary analytic methods. 

 Nor did color reactions apart from those with iodine and certain aniline dyes, nor the 

 physical and physico-chemical properties of starch-pastes and the pseudo-solutions and 

 true solutions, nor the refractive index, seem to offer opportunities for differential study 

 that were equal to those suggested by other procedures. Nor did digestion experiments 

 seem at all promising. The exceedingly contradictory data bearing on the digestibility of 

 raw starches led the author to perform a number of experiments with different starches under 

 aseptic conditions, but with negative results, as already stated. Likewise with boiled 

 starches, the many conflicting records of differences in the digestibility of boiled starches 

 of different kinds have been clearly shown by Ford, Ford and Guthrie, and by the 

 present research, to be owing to errors attending the investigations; and that, moreover, 

 as shown in the preceding chapter, so far as the degree of cUgestibility is concerned, all 

 starches from whatever source, if of equal degree of purity, may be regarded as being prac- 

 tically absolutely identical. Although our knowledge of the exact intermediate products 

 of saccharification is yet in an exceedingly unsatisfactory state, the indications are that 

 by the actions of different decomposing agents the corresponding products by these various 

 agents may differ more or less, and also that even with a given enzyme or acid under 

 given conditions they will be found, with better methods of preparation, to be different 

 in starches from various sources. At present, however, such variations as have been 

 observed in both intermediate and final products of the decomposition of starches have been 

 traceable almost invariably to the decomposing agent, and but rarely to the particidar 

 form of starch. The fact that the decomposition products from different parts of the 

 same grain differ is significant not only as to the existence of stereoisomeric forms, but 

 also of corresponding pecuUarities in the decomposition products. 



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