CONTROLLABLE DISEASE AGENTS 



335 



both the remedy and the prevention are comparatively simple. 

 The parasite can be driven from the host by the use of thymol 

 and epsom salts. Infection can be prevented by sanitary ar- 

 rangements. Where the ignorance and poverty of the people 

 permitted the soil to be polluted by human excrement, the hook- 

 worm became widely distributed in a sandy region. With the 

 installation of sanitary privies and modern toi- 

 lets the parasite comes under complete control. 



It is interesting to note that the negroes occupy- 

 ing the regions in which hookworm is common seem 

 to suffer little or no injury from the parasite. It is 

 believed that these organisms were first introduced 

 into this country through the slaves brought from 

 Africa in years past. Ahhough the negroes may 

 be infected, they appear to be immune to the seri- 

 ous damage produced by the parasites in white 

 hosts. The reason for this is not clear, but similar 

 racial differences in susceptibihty to disease have 

 been noted in regard to other parasites. Fig i-g. The tick 



This cousin of the 

 spiders has been con- 

 victed of carrying 

 dangerous disease 

 germs by biting man 

 and other mammals. 

 a, female; h, male 



252. Ringworm. The skin disease known as 

 ringworm is due to a moldlike fungus (see page 79, 

 Branch I, C) and has nothing to do with worms. 

 The irritation and damage are annoying and un- 

 pleasant, but not serious. Treatment should be 

 left to a physician, and persons who are infected 



should keep away from others, to prevent the spread of the parasite. 



253. Itch mite. Apart from the often extreme irritation caused by 

 itch, its chief danger is that the great temptation to scratch may lead to 

 infection by some more dangerous parasite. The Httle animal that 

 causes the itch is a mite, which is a nearly invisible relative of the 

 spiders. The prevention of itch is largely a matter of personal cleanliness. 



254. The tick. Another skin parasite related to the spiders is the tick, 

 which is about an eighth of an inch long. This is a bloodsucker which 

 may produce a painful bite, but its greatest danger is as a possible car- 

 rier of disease germs. The spotted fever (or Rocky Mountain fever) is 

 known to be transmitted by this animal in man, and another species 

 transmits the Texas cattle fever, which has been a very expensive 

 scourge in this country (Fig. 158). 



