BACTERIA IN DISEASE 35 



tion and supervision of dairies, milk depots, and other 

 sources of milk and cream supply. 



Food. Uncooked foods may carry infection. Raw 

 oysters, which are sometimes fattened on sewage, are 

 a prolific source of typhoid infection. Celery, lettuce, 

 radishes, and fruits are occasional sources of infection, 

 especially if exposed to dust and flies. 



Flies, because of their pernicious habit of alighting 

 upon and feeding upon all manner of filth and dis- 

 charges, are a most formidable source of infection of all 

 kinds, and especially of typhoid fever. Cholera, diph- 

 theria, tuberculosis, scarlet fever, and other infections 

 may frequently be traced to flies. 



Fleas, bed-bugs, and ticks are less frequent sources of 

 infection. The flea transmitting bubonic plague from 

 rats to rats and from rats to man, while the tick is the 

 source of infection of a disease peculiar to certain moun- 

 tainous districts of Montana, Wyoming, and Idaho, 

 called spotted fever. It is also the cause of Texas fever 

 in cattle. 



Dogs and Cats. These, as well as tame rabbits, 

 guinea-pigs, and other domestic pets, may carry dis- 

 ease germs on their coats or feet. 



Rats, Mice, and Squirrels. Rats are the great source 

 of infection in bubonic plague, having the disease them- 

 selves and scattering it broadcast by means of the fleas 

 with which they are infested. Ground squirrels have 

 recently been found to be susceptible to plague, and 



