10 



ECONOMIC ZOOLOGY 



almost eliminated while the Americans were at work 

 Canal Zone is now as healthy as almost any part of the 



Another disease that may be caused by a protozoan 

 quite certainly transmitted by one or more species 

 dengue or break-bone fever, common in many parts of 

 is a disease that causes suffering, but seldom death. 



Kala-azar or dum-dum fever is a very dangerous 

 that is supposed to be due to a protozoan parasite, 

 man by the common bedbug of India. 



there, and the 

 United States. 

 parasite, and is 

 of mosquito is 

 the tropics. It 



tropical disease 

 transmitted to 



FIG. 6. Tests of foraminifera, magnified about 10 diameters. 



Protozoology.) 



(After Calkins, 



Infusoria. This well-known and zoologically interesting class of 

 ciliated protozoa, represented by the commonly studied form Para- 

 mecium, is of little economic importance. Infusorial earth, used 

 in making dynamite, is not made up of infusoria, as might be ex- 

 pected, but of the tests of diatoms and other forms. 



A few of the infusoria may be concerned in some of the intestinal 

 diseases. 



