1913] HAWKINS—MALT DIASTASE 269 
30 tubes to be tested at one time. The control tubes were prepared 
in exactly the same way as the others, except that water was sub- 
stituted for the salt solution. In order to determine whether or not 
the salt solutions alone had any appreciable hydrolytic effect upon 
the starch, tubes were frequently made up with the salt solution 
and starch content the same as those in the experiment but without 
the diastase. These were placed in the water-bath together 
with the other tubes and tested from time to time in the usual 
manner, but in no case was there any variation from the typical 
blue color of the starch-iodine reaction. It was thus clear, as was to 
be expected, that while the salts could influence the velocity of the 
action of the diastase on starch, they were themselves apparently 
incapable of any appreciable hydrolytic action. 
To determine whether the contents of any given tube had 
teached the end point, a single drop of the stock iodine solution was 
placed in each of two small vials (ro mm. in diameter and 70 mm. 
high). To one vial was added 1 cc. of water and to the other a like 
quantity of the mixture from the proper tube, carefully pipetted out. 
The two vials were then observed against a white background in 
diffused light, and if their contents appeared to be of the same color 
(a pale yellow) the experimental end point was considered to have 
been attained. It has been found that by this method of determin- 
ing the end point, the color produced in a starch paste containing 
but 0.0002 of 1 per cent can be readily detected. This sensitive- 
ness lies well within the limits of error of the other operations of 
the experiments. Final failure of one of the starch-diastase 
mixtures to produce color (blue, purple, red, brown, etc.) does not 
necessarily mean that all of the original starch content has been 
converted into a reducing sugar, but merely that all of the starch 
has been so altered as to be no longer able to form colored com- 
pounds with iodine—showing that one or several of the steps of the 
process of hydrolysis have been completed. In this connection it 
may be remarked that Lanc® has shown with pancreatic amylase 
that the amount of a reducing sugar present at the time when the 
starch paste first fails to color with iodine does not represent and 
G, S., Uber die Einwi der Pank f Stirkearten verschie- 
denen Heskoatt Zeitschr. Exper. Path. u. Therapie 8: 279-307. 1910. 
