Page:Popular Science Monthly Volume 83.djvu/178

174 by them and their descendants should hatch into a maggot that would mature into a fly) at their normal rate of increase under favorable conditions, about one hundred trillions of flies, at a conservative estimate, or fifteen millions of tons, by weight.

Of course many flies fail to reach maturity and only a small percentage of the eggs laid ever hatch. This statement has been introduced here merely to show how ineffectual is our warfare against animals procreating their kind at such a rapid rate, as contrasted with the effect of slaughtering a few slow breeding animals. Yet many of the microscopic organisms, both harmless and disease-producing kinds, multiply infinitely faster than the house-fly.

Down to the present generation, a rapid rate of reproduction has been the surest means possessed by any animal species of withstanding the enmity of man. Now scientific knowledge is beginning to triumph over both fecundity and small size. Mosquitoes have been exterminated by the wholesale in the canal zone. Europe, Asia, Africa and Australia have been successfully ransacked to find natural enemies that will hold in check scale insects, and codling and gipsy moths. A partially successful attempt has been made to inoculate rats with a disease that will kill them as cholera once killed men. War is being successfully waged on the germs of tuberculosis, yellow fever and many other diseases, and men best qualified to judge look confidently forward to a day when not one of these infinitesimally small but infinitely baneful organisms shall exist among civilized peoples.

Under this head we may group several more or less distinct kinds of traits. First, there is the gregarious instinct, the tendency to herd together so noticeable in many animals. "In union there is strength" seems to be a motto in the animal as well as the political world. By banding together into great herds the bison became invincible to all foes save man. But with the advent of civilized man, armed with breech-loading rifles, the herding instinct of the animal only made its slaughter the more easy. The same is true, to a greater or less extent, of many other animals. Colonel Roosevelt says that, "the elk is the most gregarious of the deer family," and it was also the first of its family to disappear before the advance of civilization in almost every section of the country.

In the early seventies, passenger pigeons occupied a vast breeding ground in Michigan. It is said that in many square miles of this thickly wooded area, there was not a tree without a brooding pigeon on its nest at the proper season. Pot hunters found the birds, killed them with hands and sticks and guns, packed them in barrels and shipped