Localities in which Pellagra is Prevalent. 



61 



The mites are the young of red species belonging to the 

 genus Trombidium. They enter the skin to complete their 

 development, but appear to be unable to do this on human 

 beings. Their habit of making the attempt seems to be 

 one of nature's mistakes, for all of those entering the human 

 skin die there. Women and children often suffer -greatly 

 from the attacks, probably because of their more tender 

 skin. Men constantly living in the infested regions become 

 more or less completely immune, either because their skins 

 become tough and thick, or because they do not from long 

 exposure to the attacks become inflamed by the presence of 

 the imbedded mites. The fact of importance, however, 

 from the point of view here taken is that the mites do not 

 attack a person subsequent to an attack upon another, and 

 hence cannot well be concerned in carrying skin diseases 

 from ill to well. 



Clearing away close-growing vegetation by mowing, or 

 by fire, is a good way to get rid of them about premises. 



PROTOZOA. 



The microscopic unicellular organisms of this sort, were, 

 of course, common in all the waters. Water taken from the 

 river and brought to Lexington in jars was found to contain 

 large numbers of several species. A large ciliate species in 

 a general way resembhng Paramoecium, was extremely 



Fig. 24.— Hind tarsus of the water strider, Rhagavelia obesa, with expanded oar, and' a 

 cluster of stalked Protozoans attached. Greatly magnified, as seen under;; the 

 microscope. 



