i74 THE POPULAR SCIENCE MONTHLY 



by them and their descendants should hatch into a maggot that would 

 mature into a fly) at their normal rate of increase under favorable con- 

 ditions, 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 per- 

 centage of the eggs laid ever hatch. This statement has been intro- 

 duced here merely to show how ineffectual is our warfare against ani- 

 mals 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 extermi- 

 nated 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 par- 

 tially successful attempt has been made to inoculate rats with a dis- 

 ease that will kill them as cholera once killed men. War is being suc- 

 cessfully 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 bane- 

 ful organisms shall exist among civilized peoples. 



Mental Traits 



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 Boosevelt says that, " the elk is the most gre- 

 garious 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 



