396 
CHEMISTR Y OF THE DIGESTIVE PROCESSES. 
specific rotatory powers and reduction coefficients ; but they scarcely give 
adequate proofs that they are describing pure substances. 1 They found that 
even after twelve months a portion of the dextrin remained unconverted into 
maltose, and the substance so remaining was unfermentable by yeast. This 
substance is y-achrobdextrin, and is formed together with some maltose by the 
splitting up of /3-achrobdextrin, which in its turn is formed by a similar 
decomposition of a-achrobdextrin. 
The following is a summary of their results: — 
atory Power. 
Relative reducing 
Power for Fehling's 
Solution. 
Reaction with 
Iodine. 
Soluble starch .... 
Erythrodextrin 
«-Achroodextrin 
/3 ,, .... 
y » .... 
Maltose ..... 
Grape -sugar .... 
218" 
210° 
190° 
150° 
150° 
50° 
6 
12 
12 
28 
66 
100 
Reddish blue. 
Red. 
No coloration. 
!) 
The digestion of starch by diastatic enzymes consists of a breaking 
up, through several more or less well-defined stages, by a process of 
gradual hydrolysis, of a very complex molecule into a much simpler one, 
and might be represented schematically by the following general 
equation, which cannot be made more definite, because we are un- 
acquainted with the molecular weights of starch and dextrin, only 
knowing that they are very large — 
Starch 
Maltose 
Dextrin 
(C 6 H. 10 O 5 ) n + (H 2 0) m = ^C^A.Hp) + n ~ (C^ A>,, 
That is, starch and water, in presence of a suitable ferment, yield 
maltose and different dextrins, but we are ignorant of the value of 
n, m, and p. 
Attempts to carry too far the analogy between the action of 
dilute mineral acids and that of the diastatic ferments on starch, 
led, as already stated, to an error, which persisted for several years, 
as to the products of the latter action. Nevertheless, a close analogy 
does exist between the two processes ; both are essentially hydration 
processes ; and in both the same stages may be observed. They 
only differ in two respects, first, that the dilute acid at boiling tem- 
perature acts much more rapidly; secondly, that it proceeds a 
stage further, and very rapidly converts the maltose formed into grape- 
sugar. 
These successive changes may be best observed by boiling with very 
dilute acid ("2 per cent, or less). Soluble starch is first formed, giving, on 
neutralisation, a blue with iodine ; next, is an intermediate stage, in which a 
violet is obtained followed by a stage giving a red colour (erythrodextrin) : 
and finally a stage is reached at which a coloration is no longer obtained 
1 According to Brown and Morris (see Trans. Chan. Sue, London, 1885, p. 527 ; 1889, 
p. 462), the chemical and physical properties of these different achroodextiins might be 
given by a variable mixture of one achroodextrin possessing no reducing power with mal- 
tose. They admit the existence besides achroodextrin, of maltodextrin (Herzfeid), a body 
intermediate between achroodextrin and maltose, but more nearly allied to the latter. 
