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 cooperation 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. [Illustration: 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.