PARASITES FREE DURING THEIR WHOLE LIFE. 



131 



them produces a disease known in every country and at 

 all times- under the name of 

 the itch ; until 1830 its true 

 nature was still unknoA^T:!. It 

 is' not an affection of the skin, 

 as was thought, but merely 

 the result of the presence of 

 these animalcules. The di- 

 rector of the special Hospital 

 for Skin Diseases at Paris was 

 so fully convinced that the 

 acaridae are not the cause of 

 the itch, that he offered a 

 prize to any one who could 

 render these insects visible. A student of medicine, a 



Fig. 21.— Sarcoptes scabiei, or male 

 acarus of the itch ; the lower 

 surface. 



Fig. 22,— Sarcoptes scabiei, female ; the upper surface. 



