The Romance of Modern Chemistry

SUGAR AND STARCH Again, the conversion of starch into sugar is a chemical change of which the reader himself is the scene. As already pointed out, much of our common food contains carbohydrates, and of these starch is the one which is present in the largest proportion. Now starch itself con- sists of fine granules which are insoluble in cold water. On this account any form of starchy food should first be boiled, or baked in the presence of moisture. This treat- ment secures the bursting of the granules; they are dis- solved or at least softened, and are so rendered amenable to attack by the digestive juices. This attack begins in the mouth, where a ferment, lying in wait in the saliva, begins the conversion of starch into sugar, a process which is completed by the juices in other digestive organs. This important ferment in the saliva is not developed until several months after birth ; the disadvantage, there- fore, of giving starchy food to infants will be apparent. If such food is given it is not assimilated, for all other carbohydrates must be converted into glucose if they are to be made available for the nourishment of the body. For the further utilisation of the glucose the liver is responsible, and if this organ is not doing its duty, the sugar goes through the body unchanged and unassimi- lated ; the presence of glucose in the urine is, in fact, taken as evidence of diabetes. In cases of this disease the patient should abstain from the use not only of sugar itself, but also of all starchy food-stuffs, for these latter, as we have seen, are rapidly converted into glucose by the digestive juices. Another interesting carbohydrate which is worthy of mention is dextrin, or British gum. This compound is a sort of half-way house between starch and glucose, and is 234