ANIMALS AS DISEASE CARRIERS 401 



contract it die. The germ does not seem to have any 

 injurious effect upon the health of the rat. The flea, 

 which is an external parasite of the rat, will carry the 

 Black Death germ from the rat to man when it takes a 

 meal from the rat and then an occasional one from man. 

 This was proved in 1907, when 150,000 rats were dissected 

 in San Francisco. In order to rid the city of San Francisco 

 of the Bubonic plague and also of the rat, hundreds of 

 thousands of dollars were spent. Ten million pieces of 

 poison were laid, and it is supposed that more than two 

 million rats were killed and washed out into San Fran- 

 cisco Bay. It is considered by some that the enemy 

 Black Death, which was gaining entrance into the United 

 States through San Francisco, was more dangerous than 

 the combined army and navy of the most powerful nation 

 of the world. In Havana, in 1914, twenty city squares 

 were depopulated and the rats driven out in order to erad- 

 icate the germs of the Bubonic plague. In order for man 

 to be secure from the Bubonic plague it will be necessary 

 for him to make war on the rat until it is exterminated. 

 277. The Hog. --The hog carries two parasites which 

 affect the health of man: viz., the tapeworm and the 

 trichina. The eggs of the tapeworm are eaten by the 

 hog. These hatch within its stomach and pass through 

 the walls of the digestive organs and find their way into 

 the muscle of the hog. If these microscopic worms in the 

 muscle of the hog are eaten by man while the meat is 

 uncooked, the worm will be released by the digestive 

 juices and will attach itself to the walls of the digestive 

 organs and become a parasite of man, where the worm 

 increases in length and width, sometimes attaining a 

 length of 40 feet. A tapeworm can also be taken into 

 the body from raw beef and mutton. 



