How would a film of kerosene probably affect it? After three days the flying mosquito comes out of the pupa skin. We can free ponds of mosquito wigglers by putting a film of kerosene upon them, or by stocking them with fish, which will eat the wigglers. The mosquito is a nuisance because it makes life so disagreeable for us out of doors in summer; but it is also a disease-bearer, like the fly. One kind of mosquito carries malaria; another carries yellow fever. If the malaria-carrying mosquito inserts its sharp snout, or proboscis (prō-bŏs'Is), into a blood vessel of a person who has the disease, the germs of malaria pass into the mosquito's body with the blood which it consumes. There they multiply, and when the mosquito bites another person, the germs enter that person's blood, and give him the malaria. The yellow fever of Cuba and the Panama Canal Zone was almost entirely driven out, when the breeding places of mosquitoes were destroyed, and when the persons who were sick with the disease were screened off with great care, so that mosquitoes could not bite them and get germs to carry to other persons. 351. Exercises. 1. Give all the proofs you can think of to show that other animals as a class are harmful to man; then give all the evidence you have to prove that they are helpful. 2. Out of what material does the spider spin its web? The silkworm its cocoon? 3. What animal skins have been used as bottles? As substitutes for paper? As book coverings? As clothing? 4. What is the meaning of pecuniary"? It comes from the Latin word pecunia, meaning cattle; how do you suppose this came about? 5. Can you think why the polar bear and many other polar animals are white? What is meant by "protective coloring "? 6. Name some of the valuable breeds of dairy cows. of the milk is present in cheese? In butter? What part 7. Name some of the common breeds of chickens, and describe them. 8. Do you know of any insects which have a shape or color that make them hard to find in the surroundings in which they live? 9. What are the harmful insects which you know are living in your locality? What is being done to control or destroy them? Summary. Zoology is the science of animals. The domestication of animals and plants was important for man in his efforts toward civilization. The Eastern Hemisphere had better beasts of burden than the Western. Man's food supply has been changed greatly by cold storage and rapid transportation. Milk is a valuable food, because it has almost every kind of material for supporting life. It must be handled and preserved with care to keep it from becoming a breeding place for harmful bacteria. Leather is the connective tissue of the true skin changed by tanning. Domestic birds are valuable as food and for their eggs and feathers. Song birds should be protected because of their songs, their beauty of color and form, their highly developed care for their young, and their destruction of harmful insects. Fish form the chief animal food of a large portion of the human race. Insects form the largest class of animals, and are probably man's greatest enemies in his effort to raise and preserve plant food. Ants, bees, and wasps have developed wonderful groups, or societies. Flies and mosquitoes often cause the spread of disease and should be destroyed. CHAPTER XXXV THE STRUCTURE OF THE BODY 352. What is the Plan of the Body? As you look at a beautiful automobile, with its engine, steering gear, lighting system, and its graceful lines, can you possibly think that it was put together out of any pieces of iron, wood, brass, copper, or aluminum that happened to be lying about? No; you know that it must have been built according to a plan, and that each piece of its wonderful mechanism was carefully made, and given just the right size, shape, and strength. The same thing is true of a locomotive, an airplane, a yacht, a sewing machine, or a watch. Is it also true of that most wonderful machine, the human body? Is there a plan of the body? What are the things which impress you most about a machine like the automobile? One of them is its power, is it not? But almost at the same instant you think of its delicate parts, and of how easily it is harmed, or put out of order. Are not the same things true of man's body? It is powerful, alert, and graceful, but it is easily injured. What is true of man is true of all living things. So, in giving living things their form, nature has had two ideas to work out: (1) How can the body of the living organism be given the most power, and the ability to care for itself? |