CHAPTER XL 

 ANIMALS AS DISEASE CARRIERS 



273. Many bacteria and one-celled animals have 

 become parasitic in their habits and live in the bodies 

 of the higher animals, producing a condition known as 

 disease. Most of these diseases can now be cured, but a 

 few still resist medical science and are very dangerous. 

 In order for man to protect himself from germ diseases it 

 is necessary for him to know how germs are carried about 

 from place to place. Some germs are carried on the out- 

 side of the bodies of animals and some are carried on 

 the inside. Those which are carried on the inside of 

 animals have a complicated life history. Part of their 

 life is spent in the animal and the other part in man. 

 There are also some many-celled animal parasites which 

 spend part of their life in domesticated mammals and the 

 other part of their life in man. These parasitic diseases 

 are obtained by eating the flesh of domesticated animals. 



274. The House Fly. The house fly is also known as 

 the typhoid fly because it carries the germ which pro- 

 duces typhoid fever. The typhoid fly, in going about in 

 various places in search of food and of places for depositing 

 its eggs, comes in contact with a great deal of filth and 

 decaying matter; here it often gets the typhoid germ on 

 some part of its body, usually its feet. It then goes into 

 the house and may walk over the food which man eats or 

 the utensils from which he eats, leaving the typhoid germ 



