INTRODUCTION. 7 



These groups were found by Cross and Bevan to "pass by imperceptible gradations 

 into a heterogeneous class of natural jjroducts which, while possessing some of the char- 

 acteristics of the celluloses proper, are so readily resolved by hydrolytic treatment that 

 they must represent a very different constitutional type or types. To this group of com- 

 plex carbohydrates the name hemicellulose has been assigned," which group is stated to 

 be readily resolved into crystalline monoses. From the foregoing data it is obvious that 

 there are certain forms of cellulose that are not strictly speaking isomeric, and that there 

 are also forms that are isomerides. Cellulose is optically active, and therefore contains 

 one or more asymmetric carbon atoms, and, as a corollary, each isomer may have a number 

 of stereoisomeric forms, the number varying with the number of asymmetric carbon 

 atoms. Reasoning from this, starch may likewise exist as groups which are not strictly 

 speaking isomeric, yet in which the molecules differ so little in their molecular and struc- 

 tural formulae as to have the essential characteristics of a given prototype; secondly, 

 each group may be made up of a number of stereoisomers; and thu-dly, the starches of 

 nature, as observed in the starch-grains of a given plant, may, as it seems certain, be vari- 

 able mechanical mixtures of two or more different chemical forms. 



The number of possible starch stereoisomers is entirely problematical. Miescher has 

 estimated that the serum albumin molecule having 40 carbon atoms may have as many as 

 a thousand million stereoisomeric forms. If we assume that the molecular weight of starch 

 is as low as 15,000, and that the molecular formula is n{CQHiQO^)n, the total number of 

 carbon atoms in the molecule is at least 550. What proportion are asymmetric is unknown, 

 but judging from the relatively high percentage in such comparatively simple substances 

 as the aldohexoses, and the striking tendency for protoplasm during the synthesis of 

 organic substances to form bodies with asymmetric carbon and asymmetric nitrogen 

 atoms, it is probable that nearly all are asymmetric. Moreover, if we conceive, as we 

 should upon the present basis of our knowledge, that the molecule is not a polymeride of 

 preformed atomic groups, but an aggregate of labile groups of ionic units, the possible 

 number of stereoisomers is absolutely inconceivable. 



It has already been pointed out that a trifling transposition of elements, groups, or 

 masses attached to an asymmetric carbon atom may cause a marked change in crystalline 

 form, and in optical, chemical, and physiological properties; and also that in stereoisomers 

 changes in the configm'ation of the molecule, however slight, may give rise to greater dif- 

 ferences than may be shown by isomerides which have entirely different structural formulaj. 

 This is a matter of the most profound fundamental importance in connection with proto- 

 plasmic processes, and in it we seem to have the key to unlocking many baffling problems 

 of physiology, toxicology, and pathology — not to speak of those of general biology; nor is 

 it necessary to enter into speculation for illustrations of such applications, because many 

 instances in literature, dating from Pasteiu-'s experiments, are at one's disposal. 



In earlier pages, experiments of Pasteur were referred to which showed the marked 

 differences in the dextro-, laevo-, and racemic tartaric acids in relation to Penicillium 

 glaucum, the dextro form being consumed, the racemic form being split into the dextro 

 and laevo forms, and the dextro form being used, but the lajvo form discarded and re- 

 maining in solution. It has since been shown that the dextro forms of glucose, mannose, 

 galactose, and fructose are fermentable, or, in other words, consumed by various kinds 

 of micro-organisms as foodstuffs; while the laevo forms are not at all or but inappreciably 

 affected. Again, when mandelic acid (racemic) is subjected to the action of Penicillium 

 glaucum the compound is split, the Itevo form is consumed, but not the dextro form; 

 whereas, in the presence of Saccharomyces ellipsoideus, the dextro form but not the laevo 

 form disappears. With glyceric acid treated with Penicillium and Bacillus ethaceticuf;, 

 respectively, the primary splitting process is the same as with mandelic acid, but the 

 Penicillium uses the dextro form and the Bacillus the laevo form. 



