Part 5

Chlorin, carbon monoxid, sulphur dioxid, and hydrocyanic acid are the gases most used for destroying rats and mice in sheds, warehouses, and stores. Each is effective if the gas can be confined and made to reach the retreats of the animals. Owing to the great danger from fire incident to burning charcoal or sulphur in open pans, a special furnace provided with means for forcing the gas into the compartments of vessels or buildings is generally employed.

Hydrocyanic-acid gas is effective in destroying all animal life in buildings. It has been successfully used to free elevators and warehouses of rats, mice, and insects. However, it is so dangerous to human life that the novice should not attempt fumigation with it, except under careful instructions. Directions for preparing and using the gas may be found in a publication entitled Hydrocyanic-acid Gas against Household Insects, by Dr. L. O. Howard and Charles H. Popenoe.

Carbon monoxid is rather dangerous, as its presence in the hold of a vessel or other compartment is not manifest to the senses, and fatal accidents have occurred during its employment to fumigate vessels.

Chlorin gas has a strong bleaching action upon textile fabrics, and for this reason can not be used in many situations.

Sulphur dioxid also has a bleaching effect upon textiles, but less marked than that of chlorin, and ordinarily it is not noticeable with the small percentage of the gas it is necessary to use. On the whole, this gas has many advantages as a fumigator and disinfectant. It is used also as a fire extinguisher on board vessels. Special furnaces for generating the gas and forcing it into the compartments of ships and buildings are on the market, and many steamships and docks are now fitted with the necessary apparatus.

RAT VIRUSES.

Several microorganisms, or bacteria, found originally in diseased rats or mice, have been exploited for destroying rats. A number of these so-called rat viruses are on the American market. The Biological Survey, the Bureau of Animal Industry, and the United States Public Health Service have made careful investigations and practical tests of these viruses, mostly with negative results. The cultures tested by the Biological Survey have not proved satisfactory.

The chief defects to be overcome before the cultures can be recommended for general use are:

1. The virulence is not great enough to kill a sufficiently high percentage of rats that eat food containing the microorganisms.

2. The virulence decreases with the age of the cultures. They deteriorate in warm weather and in bright sunlight.

3. The diseases resulting from the microorganisms are not contagious and do not spread by contact of diseased with healthy animals.

4. The comparative cost of the cultures is too great for general use. Since they have no advantages over the common poisons, except that they are usually harmless to man and other animals, they should be equally cheap; but their actual cost is much greater. Moreover, considering the skill and care necessary in their preparation, it is doubtful if the cost can be greatly reduced.

The Department of Agriculture, therefore, does not prepare, use, or recommend the use of rat viruses.

NATURAL ENEMIES OF RATS AND MICE.

Among the natural enemies of rats and mice are the larger hawks and owls, skunks, foxes, coyotes, weasels, minks, dogs, cats, and ferrets.

Probably the greatest factor in the increase of rats, mice, and other destructive rodents in the United States has been the persistent killing off of the birds and mammals that prey upon them. Animals that on the whole are decidedly beneficial, since they subsist upon harmful insects and rodents, are habitually destroyed by some farmers and sportsmen because they occasionally kill a chicken or a game bird.

The value of carnivorous mammals and the larger birds of prey in destroying rats and mice should be more fully recognized, especially by the farmer and the game preserver. Rats actually destroy more poultry and game, both eggs and young chicks, than all the birds and wild mammals combined; yet some of their enemies among our most useful birds of prey and carnivorous mammals are persecuted almost to the point of extinction. An enlightened public sentiment should cause the repeal of all bounties on these animals and afford protection to the majority of them.

ORGANIZED EFFORTS TO DESTROY RATS.

The necessity of cooperation and organization in the work of rat destruction is of the utmost importance. To destroy all the animals on the premises of a single farmer in a community has little permanent value, since they are soon replaced from near-by farms. If, however, the farmers of an entire township or county unite in efforts to get rid of rats, much more lasting results may be attained. If continued from year to year, such organized efforts are very effective.

COMMUNITY EFFORTS.

Cooperative efforts to destroy rats have taken various forms in different localities. In cities, municipal employees have occasionally been set at work hunting rats from their retreats, with at least temporary benefit to the community. Thus, in 1904, at Folkestone, England, a town of about 25,000 inhabitants, the corporation employees, helped by dogs, in three days killed 1,645 rats.

Side hunts in which rats are the only animals that count in the contest have sometimes been organized and successfully carried out. At New Burlington, Ohio, a rat hunt took place some years ago in which each of the two sides killed over 8,000 rats, the beaten party serving a banquet to the winners.

There is danger that organized rat hunts will be followed by long intervals of indifference and inaction. This may be prevented by offering prizes covering a definite period of effort. Such prizes accomplish more than municipal bounties, because they secure a friendly rivalry which stimulates the contestants to do their utmost to win.

In England and some of its colonies contests for prizes have been organized to promote the destruction of the English, or house, sparrow, but many of the so-called sparrow clubs are really sparrow and rat clubs, for the destruction of both pests is the avowed object of the organizations. A sparrow club in Kent, England, accomplished the destruction of 28,000 sparrows and 16,000 rats in three seasons by the annual expenditure of but L6 ($29.20) in prize money. Had ordinary bounties been paid for this destruction, the tax on the community would have been about L250 (over $1,200).

Many organizations already formed should be interested in destroying rats. Boards of trade, civic societies, and citizens' associations in towns and farmers' and women's clubs in rural communities will find the subject of great importance. Women's municipal leagues in several large cities already have taken up the matter. The league in Baltimore recently secured appropriations of funds for expenditure in fighting mosquitoes, flies, and rats. The league in Boston during the past year, supported by voluntary contributions for the purpose, made a highly creditable educational campaign against rats. Boys' corn clubs, the troops of Boy Scouts, and similar organizations could do excellent work in rat campaigns.

STATE AND NATIONAL AID.

To secure permanent results any general campaign for the elimination of rats must aim at building the animals out of shelter and food. Building reforms depend on municipal ordinances and legislative enactments. The recent plague eradication work of the United States Public Health Service in San Francisco, Seattle, New Orleans, and at various places in Hawaii and Porto Rico required such ordinances and laws as well as financial aid in prosecuting the work. The campaign of Danish and Swedish organizations for the destruction of rats had the help of governmental appropriations. The legislatures of California, Texas, Indiana, and Hawaii have in recent years passed laws or made appropriations to aid in rat riddance. It is probable that well-organized efforts of communities would soon win legislative support everywhere. Communities should not postpone efforts, however, while waiting for legislative cooperation, but should at once organize and begin repressive operations. Wherever health is threatened the Public Health Service of the United States can cooperate, and where crops and other products are endangered the Bureau of Biological Survey of the Department of Agriculture is ready to assist by advice and in demonstration of methods.

IMPORTANT REPRESSIVE MEASURES.