122 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



has been establislied tliat plague is primarily a rat disease and that 

 it is transmitted to human beinf:;s cliielly by the agency of the fleas 

 which infest rats, this aspect of the problem has quite overshadowed 

 the purely economic side of the matter, important as that is. Dur- 

 ing the year experiments with traps and poisons were conducted, 

 these being the chief present available means for reducing the num- 

 ber of noxious rodents. So great are the rat's productive powers, 

 however, that imless these measures are persistently and energetic- 

 ally pushed the relief obtained is only temporary. It can not be too 

 strongly emphasized, therefore, that permanent freedom from the 

 pest can be secured only by preventive measures. When a building 

 is infested by rats, it can be freed from the vermin by stopping means 

 of ingress, usually not diflicult nor expensive, and then depriving the 

 animals of food, when they can be easily trapped. What is true of 

 single buildings is true of cities and communities. When the public 

 is educated to the importance of withholding all food supplies from 

 rats, and when buildings are made practically rat proof, a very long 

 step will have been taken toward the solution of the rat problem. 



Inasmuch as requests from various parts of the country as to the 

 effectiveness of bacterial preparations for destroying rats continue to 

 be received, the results of experiments of the Survey with several 

 such preparations now on the market may be repeated. When fresh 

 and virulent, the preparations can usually be depended on to kill the 

 individual rats eating the prepared baits, but they do not set up, as 

 has often been claimed, an epidemic among the rodents. They are 

 hence regarded as inferior to poisons because of their uncertainty of 

 action, ineffectiveness, and cost. The cost indeed is practically pro- 

 hibitive when the preparations are required to be used on a large scale. 



CALIFORNIA GROUND SQUIRREL. 



The California ground squirrel continues to be the subject of 

 important field investigations because it annually destroys millions 

 of dollars worth of grain, fruit, and nuts, and because it tunnels in 

 irrigation embankments. Thus in May, 1910, ground squirrels caused 

 such a serious break in the Turlock Canal in Stanislaus County that 

 the cost of the necessary repairs amounted to $25,000. As the repair 

 work occupied some tliree months, the ranchers were deprived of 

 water at the very season when most needed, the resulting loss of crops 

 being estimated at upward of a half million dollars. Still more 

 important is the fact that this squirrel has become plague-stricken. 

 Already three or four persons are known to have been infected with 

 plague from squirrels. The real significance of the spread of plague, 

 however, to this wild mammal is not so much the present danger of 

 infection of a greater or less number of persons, but the fact that 

 unless vigorous steps are taken the disease is Hkely to become per- 



