75 
ferments. Prominent among these are diastase, one of the enzymes de- 
veloped in the germination of grains; ptyalin, a characteristic constituent 
of saliva, and pancreatin, secreted by the pancreas. So far as the diges- 
tion of starch is concerned these are probably the principal agencies 
which change starch from its natural, insoluble form into the soluble and 
digestible modifications, and a study of their action upon starches ought 
to throw considerable light upon the comparative degrees of resistance of 
different starches to digestive action. 
Such studies have been made with the codperation of several students 
and at different times, leading to results which seem of general interest 
and application. As material for one study we selected the starches of 
wheat, maize, rice, the common potato and the sweet potato, as represent- 
ing not only important food articles, but starches of different botanical 
character. 
These were prepared in the laboratory in preference to using commer- 
cial preparations, with the attendant risk of adulteration. Moreover, 
acids and alkalies are commonly used in the preparation of the starch 
of commerce, and undoubtedly affect its character. The five kinds of 
starches were prepared by grating or grinding the raw materials, agitating 
with cold water, straining through coarse muslin and afterwards allow- 
ing the starch to settle from suspension in water after frequent washings. 
The materials thus obtained were probably quite pure starches, and at 
least were sufficiently free from impurities or foreign matter to satisfac- 
torily serve the purpose of the experiment. 
The plan of the investigation was to subject the different starches 
under identical conditions to the action of a ferment, and note the time 
when each kind of starch had been completely dissolved. As an indica- 
tion of this result the well-known action of starch and iodine was em- 
ployed. When the starch preparation no longer showed the blue color 
with iodine it was regarded as completely dissolved or changed. 
Exactly stated, it was endeavored to obtain an identical physical con- 
dition of all the starches, and then to expose them under constant condi- 
tions of temperature and dilution to a uniform solution of the enzyme or 
digestive ferment. 
A weighed quantity of the starches, one gram, or in some cases one- 
half gram, was heated with 50 or 100 cubic centimeters of distilled water 
in a boiling water bath during 30 minutes and then cooled to 65° C. An 
infusion of malt was made by digesting five grams of malt with 200 ¢. c. 
