A Civic Biology, Presented in Problems

by George W. Hunter

To rid a house of fleas we must first find their breeding places. Old carpets, the sleeping places of cats or dogs or any dirty unswept corner may hold the eggs of the flea. The young breed in cracks and crevices, feeding upon organic matter there. Eventually they come to live as adults on their warm-blooded hosts, cats, dogs, or man. Evidently destruction of the breeding places, careful washing of all infected areas, the use of benzine or gasoline in crevices where the larvæ may be hid are the most effective methods of extermination. Pets which might harbor fleas should be washed frequently with a weak (two to three per cent) solution of creolin.

Bedbugs are difficult to prove as an agent in the transmission of disease but their disgusting habits are sufficient reason for their extermination. It has been proven by experiment that they may spread typhoid and relapsing fevers. They prefer human blood to other food and have come to live in bedrooms and beds because this food can be obtained there. They are extremely difficult to exterminate because their flat body allows them to hide in cracks out of sight. Wooden beds are thus better protection for them than iron or brass beds. Boiling water poured over the cracks when they breed or a mixture of strong corrosive sublimate four parts, alcohol four parts and spirits of turpentine one part, are effective remedies.

How the Harm done by Insects is Controlled.—The combating of insects is directed by several bodies of men, all of which have the same end in view. These are the Bureau of Entomology of the United States Department of Agriculture, the various state experiment stations, and medical and civic organizations.

The Bureau of Entomology works in harmony with the other divisions of the Department of Agriculture, giving the time of its experts to the problems of controlling insects which, for good or ill, influence man's welfare in this country. The destruction of the malarial mosquito and control of the typhoid fly; the destruction of harmful insects by the introduction of their natural enemies, plant or animal; the perfecting of the honeybee (see Hodge, Nature Study and Life, page 240), and the introduction of new species of insects to pollinate flowers not native to this country (see Blastophaga, page 43), are some of the problems to which these men are now devoting their time.

All the states and territories have, since 1888, established state experiment stations, which work in coöperation with the government in the war upon injurious insects. These stations are often connected with colleges, so that young men who are interested in this kind of natural science may have opportunity to learn and to help.

The good done by these means directly and indirectly is very great. Bulletins are published by the various state stations and by the Department of Agriculture, most of which may be obtained free. The most interesting of these from the high school standpoint are the Farmers' Bulletins, issued by the Department of Agriculture, and the Nature Study pamphlets issued by the Cornell University in New York state.

This diagram shows how bubonic plague is carried to man. Explain the diagram.

Animals Other than Insects may be Disease Carriers.—The common brown rat is an example of a mammal, harmful to civilized man, which has followed in his footsteps all over the world. Starting from China, it spread to eastern Europe, thence to western Europe, and in 1775 it had obtained a lodgment in this country. In seventy-five years it reached the Pacific coast, and is now fairly common all over the United States, being one of the most prolific of all mammals. Rats are believed to carry bubonic plague, the "Black Death" of the Middle Ages, a disease estimated to have killed 25,000,000 people during the fourteenth century. The rat, like man, is susceptible to plague; fleas bite the rat and then biting man transmit the disease to him. A determined effort is now being made to exterminate the rat because of its connection with bubonic plague.

Other Parasitic Animals cause Disease.—Besides parasitic protozoans other forms of animals have been found that cause disease. Chief among these are certain round and flat worms, which have come to live as parasites on man and other animals. A one-sided relationship has thus come into existence where the worm receives its living from the host, as the animal is called on which the parasite lives. Consequently the parasite frequently becomes fastened to its host during adult life and often is reduced to a mere bag through which the fluid food prepared by its host is absorbed. Sometimes a complicated life history has arisen from their parasitic habits. Such is seen in the life history of the liver fluke, a flatworm which kills sheep, and in the tapeworm.