96 



The National Geographic Magazine 



Photo by Bailey, Biological Survey 



GRAY r'OX — NEW MEXICO 



Study of the use of epidemic diseases — 

 nature's own method of destro3'ing sur- 

 plus population. It has long been known 

 that at irregular intervals, when mam- 

 mals, especially rodents, that live in 

 crowded communities increase till they 

 are very numerous, they are suddenly 

 smitten with an epidemic which almost 

 wipes out the species over a considerable 

 area. In the case of such epidemics a 

 certain number of individuals either are 

 immune to the disease or recover from it ; 

 for while nature is prodigal with the lives 

 of individuals and wastes them with ap- 

 parent recklessness, she cherishes the 

 species and is chary of exposing one to 

 the risk of elimination. After a few years 

 the animal that has paid the price of too 

 great prosperity again multiplies beyond 

 limits, to be again reduced. 



Efforts are now being made to obtain 

 cultures of the diseases which prevail 

 among the more destructive of our ro- 

 dents, so that they may be employed in 

 other regions where the animals are pests. 

 Since the cultures mav be renewed from 



time to time, they can be kept indefinitely 

 and be ready for use as required. If they 

 prove as effective as when employed by 

 nature, the problem of a cheap and re- 

 liable method of dealing with destructive 

 rodents will have been solved. 



FOX FAEIIING 



Time was when it might almost have 

 been said that America furnished furs for 

 the world, and even now no inconsider- 

 able part of the fur harvest comes from 

 America. Year by year, however, the 

 harvest is diminishing, while the price of 

 furs is steadily advancing, till the finer 

 and rarer kinds are within the reach of 

 only the very wealthy. Foxes of the more 

 valuable kinds, for instance, once so nu- 

 merous in this country, are now compara- 

 tively scarce. Their fur is so valuable 

 and so much sought for that, instead of 

 trying to discover means to compass their 

 destruction, the Survey is now studying" 

 the best methods of fox farming, with a 

 view to making the breeding of the 



