Arthropods and Disease Transmission 353 



alimentary canal of most roaches fifteen hours after feeding them 

 untold millions of viable cells. This indicated that passive transfer 

 of typhoid organisms on the outer surfaces of these roaches is more 

 siejnificant than the excretion of these bacteria by Blattella ger- 

 manica. It is this type of finding that indicates the importance 

 of carefullv controlled studies before sweeping statements are made 

 concerning roaches as vectors of disease. 



MOSQUITOES 



The discovery of Sir Ronald Ross in 1897 that malaria is a 

 mosquito-transmitted disease, and the finding of Walter Reed in 

 1900 that yellow fever virus is spread by the mosquito Aedes 

 aegifpti have provided us with technics for attacking the problem 

 of control of these diseases. If breeding grounds are destroyed, 

 the mosquito population will drop. Smaller numbers of infected 

 persons will furnish fewer possible sources of infectious material 

 for the biting mosquitoes. It is the female of the species, inci- 

 dentally, that does the biting. 



Other diseases which may be transmitted through the bite of 

 various mosquitoes include the virus of dengue fever (also called 

 breakbone fever), and the endemic disease filariasis found in 

 tropical and in semi-tropical countries. Filariasis is caused by a 

 threadworm which occludes capillaries and lymphatic vessels caus- 

 ing a condition known as elephantiasis. 



TICKS 

 Since ticks have eight legs, they are not considered to be true 

 insects. Ticks are found on many animals, including dogs, and a 

 walk through the underbrush in many areas will result in a person 

 picking up ticks on his clothing. Not all ticks harbor pathogenic 

 organisms, but care should be exercised in removing ticks which 

 have embedded themselves in the skin. The lighted end of a 

 cigarette or a lighted match when applied to the posterior end of 

 an imbedded tick will usually convince the arthropod that he 

 should back out. A little chloroform applied on the tick will 

 usually accomplish the same results. It is inadvisable to try to pick 



