iij:\<>s/:s G,')! 



ciplos coininoii to all. l-Aiun'malion of tlic S toiiimhu' sIkiws tlial iiiiinhLTs 1 2, 

 4 and .> have aldfliydc fjroiijjs ( 11 — C^ O) at tlic end of the eliaiii and arc licncc 

 aldolii'xoscs. Mcndici's :? and t> have kctom- (C^f)) >rroii,))s, at tlic second car- 

 bon atom, and are therefore 2-keto-liexoses, while numbers 7 and S havinjj ketone 

 jjroups at the third carbon atom are .'5-keto-hcxoses. Since each series of S sugars 

 has a like nnmber of the diircrcnt types there are in all Iti aldoln-xoscs. ci^lit 2-keto- 

 and ciiiht ;i-keto-liexoses. 



Jt had lonjr been known that if a solution of any optically active su^'ar. such 

 as d-jihicose. was alkalini/.ed the solution <iradually lost its optical activity. It 

 was later shown by Lol)rv de Bruyn and van Ekcnstein that a solution of 

 d-jrhu'ose in very dilute alkali coines to contain a tjroup of 4 hexoses in dynamic 

 chemical equilibiiuni.-'i- Ncf -" held that in such solutions there is an e(piili- 

 brium of at least eiijlit hexoses as above depicted. Any one of these sugars when 

 placed in alkali reproduces the other seven, since the members of the series are 

 reciprocally convertible one into another. The same holds good for the members 

 of the d-galactose series and for tlu^ 1-galactose and l-glucoae series. Rut the 

 reciprocal transformation of tlie members of one series, such as d-glucose, into a 

 hexose of another series, such as d-galactose. occurs, if at all, only to a minute 

 degree, because sucli transformation involves the breaking of the hexose chain into 

 2, '.i and 4 carbon fraiiinents with subse(|uent recombinations, and wlien this 

 occurs irreversi])le reactions are prone to intervene. The formation of lactic 

 acid and the saccharines aie rej)resentative of these irreversible reactions. (In 

 the body, however, glucose may be converted into lactic acid in the muscles and 

 elsewhere, whereas in diabetes lactic acid can be converted easily back intc 

 glucose; in diabetes galactose is convertible into glucose, etc., so that in the 

 body the transformation of hexoses of ditferent groups one into another offers no 

 difficulty. ) 



In order to explain the effects of dilute alkali on hexoses just described, some 

 conception of labile intermediate products is a logical necessity, for when levulose 

 changes into glucose there is necessarily some intermediate phase. The nature of 

 these phases has been the subject of study by many chemists, and this study 

 involves always the question of sugar dissociation. 



Sugars are weak acids. They form salts with metals, and Cohen 28 and later 

 Michaelis and Rona 20 have determined by physico-chemical methods the ioniza- 

 tion constants for glucose and other sugars. Sugars are also polyatomic alcohols, 

 and either aldehydes or ketones. Sugar chemistry reverts to the chemistry of 

 these three classes of compounds. 



A. P. Mathews so and ]Michaelis have suggested that the effect of alkali on a 

 siiffar such as srlucose is to increase enormouslv the concentration of the gh;cose 

 anion, i. e., KOH leads to the formation of K-glucosate (see Fig. 3, p. 21), which, 

 being the combination of a powerful base with a very weak acid, has a high 

 electrolytic dissociation constant. These anions accordinir to this view are sub- 

 ject to cleavages and intramolecular rearrangements. Nef also holds that the 

 first effect of the alkali (c. jr., KOTI) is to form a salt, but his far more detailed 

 conception of the subseciuent changes which lead to reciprocal transformations 

 of hexose sugars one into another, involves other principles which represent the 

 outsiTowth of his earlier work on the properties of simpler aldehydes aiul ketones. 



These reciprocal transformations are dependent, according to Xef, ujion the 

 aldehydic or ketonic character of the sugar, whereas the oxidative phenomena and 

 the saccharinic acid formation to be described presently, depend upon the alcohol 

 groups. The principles involved can best be understood if we first consider the 

 behavior of a simple aldehyde (acetaldehyde) and a simple ketone (acetone). 

 Acetaldehyde in the presence of water forms a hydrate (comparable to chloral 

 hydrate) . 



"oRec. trav. cliim. de Pays Pas (14), l-'iS and 203: d.",), 92: (IG). 2r,7: (10). 

 1 and 10. 



2- Liebig's Annalen. 1007 (3o7). 204: 1010 (37G), 1. 

 2sZeit. f. phvsikal. Chem., 1001 (36), 60. 

 20 Biochem. Zeit., 1012 (47), 447. 

 30 Jour. Biol. Chem., 1909 (6), 1. 



