30 



internal parasites, and the only two farm animals known to be 

 infested by them are the hog and the rat. The disease in hogs 

 is caused by eating trichinous rats or trichinous pork. Country 

 slaughterhouses, where rats are abundant, are among the chief 

 sources of trichinous pork, which if not thoroughly cooked, 

 communicates the disease to the person who eats it. Rats are 

 subject to many intestinal worms and other internal parasites, 

 and also to a kind of leprosy. Fatal so-called "septic pneu- 

 monia" is said to result sometimes from drinking water from 

 wells where rats have been drowned.^ 



Rats are disseminators of the germs of many diseases, be- 

 cause of their habits of frequenting privies, drains and sewers 

 for the food they find there. Ptomaines are likely to be con- 

 veyed to human food in this manner. Rats are numerous in 

 slums and hovels where malignant and loathsome diseases 

 flourish, and so undoubtedly they convey infections to other 

 locahties by contact with food or food receptacles. ^ledical 

 men and municipal boards of health are beginning to take 

 cognizance of the rat as a dangerous agent in the dissemination 

 of common diseases of both children and adults, but to what 

 extent, if any, this animal distributes the seeds of typhoid and 

 scarlet fevers, diphtheria and other malignant diseases, re- 

 mains for future study to determine. 



CIRCUMSTANCES FAVORABLE TO THE MULTIPLICATION 

 OF RATS AND THEIR APPEARANCE IN LARGE NUM- 

 BERS. 



Rats can increase rapidly in numbers only under the most 

 favorable conditions. As hereinbefore stated, a sudden influx 

 of rats may usually be accounted for by a sudden scarcity of 

 food somewhere, followed by migration. Rats naturally turn 

 first to vegetable food, such as nuts and seeds. Certain seeds 

 seem to be preferred by most rats to all other food, and where- 

 ever such nourishment is plentiful, rats multiply rapidly. 

 Plagues of rats occur in Brazil after the bamboo blooms. This 

 great plant matures, produces its seed and dies, at intervals of 

 several years, and according to Mr. Herbert H. Mercer the 



» The Spectator (London), Vol. 95, Oct. 21, 1895, p. 6M. 



