

192 



Dr. E. F. Armstrong. 



[Aug. 26, 



It will be noticed that the various hexosides vary widely in stability : 

 the /3-glucosides undergoing hydrolysis more rapidly than the stereo- 

 isomeric a-compounds a fact already noted by Alberda von Ekenstein 

 whilst the galactosides are more rapidly attacked than the corre- 

 sponding glucosides. These conclusions are in harmony with the well- 

 known fact that the a-compound preponderates in the mixtures 

 obtained in preparing the methyl glucosides and galactosides* and 

 also serve to explain the circumstance that, in separating methyl 

 galactoside (by E. Fischer's method), it is necessary to avoid the 

 presence of acid far more carefully than in separating methyl 

 glucoside. 



In the case of the a- and /3-glucosides and galactosides, the stereo- 

 isomerism in each pair of compounds is confined to the terminal carbon 

 atom ; it is, perhaps, noteworthy that there should be so considerable 

 a difference between compounds so related. 



But it is even more surprising that a change in the general configura- 

 tion at the fourth carbon atom, affecting only the nature of the attach- 

 ment of the oxygen atoms within the ring, such as occurs when 

 glucose passes into galactose, should have so marked an influence on 

 the activity of the group associated with the terminal carbon atom. 

 Such a result enhances the probability of the conclusion that the 

 active system within which the change takes placet is formed by the 

 association of acid- water molecules with the oxygen atom in the penta- 

 phane ring : in other words, that this oxygen atom is .the attractive 

 centre. The argument here made use of renders it desirable that the 

 behaviour of the isomeric mannosides towards acids should also be 

 studied, in order that it may be possible eventually to define more or 

 less accurately the functions of the different oxygen atoms in the 

 molecule. 



Enzyme Activity. At present, the experiments have been confined 

 to two substances, maltose and a-methyl glucoside, which both undergo 

 hydrolysis under the influence of the enzymes contained in ordinary 

 yeast maltase. 



Fifty cubic centimetres of a solution containing 5 grammes of a-methyl 

 glucoside was mixed with 50 c.c. of a maltase extract prepared from dried 

 yeast;| the mixture was kept at 22. Samples were withdrawn every 

 hour and polarimetrically examined. Considerable difficulty was at 

 first experienced in obtaining sufficiently clear solutions for this purpose, 

 owing to the impossibility of removing the suspended proteid matter 

 by mere filtration ; it was eventually discovered that the liquids could 

 be clarified by means of sodium acetate. The method at present 



* E. Fischer, 'Ber.,' vol. 26, p. 2400; Jungius, ' Proc. K. Akad. Wetensch.,' 

 Amsterdam, 1903, vol. 6, p. 99. 



t Compare Armstrong and Caldwell, ' Boy. Soc. Proc.,' vol. 73, p. 526. 

 J ' Koy. Soc. Proc.,' vol. 73, p. 504. 



