10 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



by mere solution in water; by a slight increase of temperature; by the action of sunlight; 

 by crystallization; by repeated recrystallization; by the actions of certain chemical agents, 

 such as traces of halogens, alkalies, certain acids, etc. 



It has been found in recent investigations that the transmutation of stereoisomers 

 can be accelerated by bases, by salts generally, and by certain acids, etc.; and inhibited 

 by alcohol, phenol, certain acids, and a number of other bodies. The readiness with which 

 such transformations may occur is instanced in the following cases: Wlien a-glucose in 

 aqueous solution is converted into i3-glucose; when maleic acid is heated slightly above 

 the melting-point and the stereoisomeric fumaric acid appears; when the benzyl-/3-amido- 

 crotonic ester is converted by sunlight into the a form; when the solution of a-methyl- 

 cinnamic acid is crystallized, yielding the j3 form; when the aceto-acetic ester phenyl- 

 hydrazone is by simple repeated recrystallization transformed into a stereoisomer having 

 a nmch higher melting-point and other differences in properties; when in the reversal 

 of the enzymic maltose-dextrose reaction isomaltose appears instead of the initial mal- 

 tose; when maleic acid is converted into fumaric acid by the agency of the combined 

 catalytic actions of sulphur dioxide and sulphureted hydrogen; and when a-glucose in 

 solution is transmuted with great rapidity into /3-glucose by the agency of a mere trace 

 of alkali, etc. 



Perhaps among all of the instances of the transmutation of stereoisomers that might 

 be quoted, none is of broader and more fundamental importance in its bearings in biology 

 than when under certain conditions there occurs a spontaneous conversion of one form 

 of glucose into another when in aqueous solution. The solution of natural glucose is that 

 of an equilibrated mixture of two stereoisomerides, a-glucose and /3-giucose, the former 

 having the lower solubility, but the higher crystallizabihty and rotatory power. The 

 rotatory power of the pure solution, as found by Dubrunfaut in 1846, lessens with marked 

 slowness, which change has been shown in recent years to be due to the transformation 

 of some of the a form into the fi form. If such a solution be concentrated until crystal- 

 lization occurs, some of the a form crystallizes out, thus causing the solution to be tlirown 

 out of equihbrium, which disturbance immediately tends to be compensated for by a con- 

 version of some of the /3 form into the a form, to replace the moiety of the latter which 

 has passed into sohd form. If, now, the preparation be warmed so as to cause a re-solution 

 of the crystaUine a form there will be a conversion of some of the a form that is in solu- 

 tion into the /3 form until equilibrium of solution is again established. If, now, we suppose 

 that only one or the other of these forms is especially adapted to the requirements of 

 protoplasm, as is to be inferred from the illustrations previously given, it is clear how 

 through such transformations there may be maintained not only an equilibrium of solu- 

 tion, which often is of such vast importance in vital processes, but also a continuous 

 sujiply of pabulum in a form that is especially adapted to nutritive exactions. 



Such instances indicate not only how readily a given form of stereoisomer may, in 

 order to meet nutritional needs, or because of casual conditions, be transmuted into 

 another form wliich may have markedly different properties, but also that inasmuch as 

 the conditions existent in living matter are of a highly favorable character to stereo- 

 isomeric transformations, that such changes are continually going on, and inferentially 

 of the greatest importance. Coupling the foregoing statements with the recognized 

 extreme labihty or unstability of protoplasm, it requu-es no effort of thought to con- 

 ceive of how the more or less marked and continual changes in conditions, internal and 

 external, to which organisms are subjected may bring about with equal or greater facility 

 transformations in the configurations of the slereochemic units of protoplasm, thus altering 

 to a greater or less extent the physico-chemical mechanism, and in turn giving rise to 

 physiological and morphological changes which may be temporary or permanent, and 

 even heritable. 



