Use as Food.—They are so numerous in lakes, rivers, and the ocean as to form the food for many animals higher in the scale of life. Almost all fish that do not take the hook and that travel in schools, or companies, migrating from one place to another, live partly on such food. Many feed on slightly larger animals, which in turn eat the Protozoa. Such fish have on each side of the mouth attached to the gills a series of small structures looking like tiny rakes. These are called the gill rakers, and aid in collecting tiny organisms from the water as it passes over the gills. The whale, the largest of all mammals, strains protozoans and other small animals and plants out of the water by means of hanging plates of whalebone or baleen, the slender filaments of which form a sieve from the top to the bottom of the mouth.
Protozoa cause Disease.—Protozoa of certain kinds play an important part in causing malaria, yellow fever, and other diseases, as we shall see later.[26] (See page [217].)
[25] Amœbæ may be obtained from the hay infusion, from the dead leaves in the bottom of small pools, from the same source in fresh-water aquaria, from the roots of duckweed or other small water plants, or from green algæ growing in quiet localities. No sure method of obtaining them can be given.
[26] Teachers may find it expedient to take up the study of protozoan diseases at this point.
Reference Books
elementary
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Davison, Human Body and Health. American Book Company.
Jordan, Kellogg and Heath, Animal Studies. D. Appleton and Company.
Sharpe, Laboratory Manual, pp. 140-143. American Book Company.