INTRODUCTION. 13 



Starch, like saccharose, is optically active in both solid state and solution. Starch 

 grains are, as a rule, markedly optically active, which activity is due in part to the 

 asymmetric molecules, and in part to the intermolccular arrangements of the starch 

 in the solitl form. If grains of potato starch, for instance, are examined in water with 

 ihe ]wlarizing microscope, and the slide be gradually heated to the minimal temperature 

 of gelatinization, it will be found that gelatinization and swelling will begin at a given 

 point or points, and that the progress of the process can accurately be traced by the cor- 

 responding disappearance of optical activity. This alteration is obviously due to a break- 

 ing down of the intermolccular structure of the grain; but the gelatinized starch is never- 

 theless still optically active. Brown, Morris, and Millar found the specific rotatory power 

 of 2.5 to 4.5 per cent concentrations of soluble starch at 15.5 C. to be (o)^ = + 202. In 

 differentiating isomcrides which are in crystalline form, the melting-point, or, in other 

 words, the temperature at which the intermolecular organization is broken down, is one 

 of the most important means of distinction. Hence, as the starch-grain is a spherocrystal, 

 the temperature of gelatinization must be regarded as being ecjually important in the 

 differentiation of starch stereoisomers. In various parts of this memoii', especially in 

 Chapters IV and VI, the various methods employed in the differentiation of starches are 

 given adeciuate consideration to meet the conditions of the investigation. 



CONCEPTIONS, METHODS, PLAN, AND CONDUCT OF THIS RESEARCH. 



Opinions may differ widely in regard to various features pertaining to the concep- 

 tions, methods, plan, and conduct of tliis research. Thus, it might be hekl that such 

 differences as have been noted in different starches might be attributable to mixtures of a 

 unit substance which may exist in multiple forms having variable physical but not chemical 

 properties, but such a view finds insignificant support in the literature of starch, or in the 

 results of this research; while, on the other hand, the evidence points positively to the 

 existence of a vast number of stereoisomers, which, however, may be multiple in the 

 starch of any species or even in any given starch-grain. As regards the methods selected, 

 choice was based in part upon the results of recorded work, and in part upon deductions 

 upon general principles. The histological method, in use for two centuries, has shown that 

 starch-grains from different plants appear in a great variety of forms, and that peculiarities 

 of form may be definitely related to the genus or species, etc. ; the polariscope has demon- 

 strated differences in the degrees of polarization, differences in the interference figure or 

 "cross," and differences in reaction in the presence of the selenite plate; iodine and anilines 

 have been found to vary in their reactions with different starches; temperatures of gelatiniza- 

 tion have been recorded by Lippmann and others as ranging within wide limits; the degrees 

 of digestibility of both raw and boiled starches are stated by different authors to vary 

 markedly; and a number of "swelling reagents" have been found to elicit differences in 

 minute histological stnicture, as well also in the intensity of action. 



In the preliminary work of this research it was found that digestion experiments, 

 whether upon raw or boiled starch, were of no value in detecting differences in the starch- 

 substance per se. Apart from this method, all of the others enumerated were used. The 

 selection of the particular anilines and swelling reagents was based to only a minor degree 

 upon the results of experience. It is quite probable, indeed almost certain, that better 

 results are to be obtained by other reagents; but this must be shown by experience. It 

 has been taken for granted that the phenomenon of swelling, whether brought about by 

 heat or chemical reagents, is a manifestation of adsorption affinity that is a specific prop- 

 erty of the starch, and variable in relation to the molecular configuration and intermolec- 

 ular structure of the different hyijothetical stereoisomers; and, conversely, that cjuanti- 

 tative and qualitative differences in the reactions to these agents are indicative of corre- 



