Diastase
a substance existing in barley, oats, and potatoes, but only after germination. When in solution it posstarch to break up at the temperature of starch to break up at the temperature of -trine and then into sugar. It is obtained by digesting in a mixture of three parts of water and one of alcohol, at a temperature of 113° F., a certain quantity of ature of 113° F., a certain quantity of the open air, and then putting the whole stase is solid, white, and soluble in water strong alcohol. general habit or constitution of body as DIATHESIS, in medicine, a certain predisposing to certain diseases. plants usually referred to the class Algæ. plants usually referred to the class Algæ. DIATOMS, an order of microscopic There are more than 4,000 distinct spe- The walls of the cells are rendered hard cies scattered over all parts of the world. by silica and they are reproduced by fission, the splitting taking place parallel to the longer axis. When the protoplasm escapes the cell walls retain their shapes and delicate markings. Enormous quantities of them are found as fossils in the beds of the Tertiary formation. Often cape and unite to form a zygospore, the protoplasm of two diatoms will eseach forming a new cell larger than bewhich after a time will divide into two, fore. Some diatoms are free and move rapidly through the water; others secrete a mucilaginous substance whereby they attach themselves to various objects. In some cases the diatoms, after splitting, remain attached to one another, forming some cases the diatoms, after splitting, bands or ribbons. according to the structure of the cell walls, three main families being recog- They are classified, nized, according as they have on the principal face of the wall a distinct ridge cipal face of the wall a distinct ridge (Pseudoraphidieæ), or no ridge at all (Pseudoraphidiez), or no ridge at all