Ordinary human scabies is caused by an arthropod (insect) of the order Acarina, a member of the family Sarcoptidae known as Sarcoptes (or Acarus) scabiei de Geer (var. hominis). As is well known, this burrowing mite is an obligatory human parasite which is specifically adapted to one host—man. In human beings the mite burrows into and within the horny layer, reaches the less cornified epidermal cells, and there derives the nutrient substances which enable it to live and to propagate. The mating and the entire life cycle of the insect take place on the human host. The result of this parasitism is the disease called scabies.
The severity both of the objective manifestations and of the itching varies greatly from person to person. This variation must be due in a great measure to the fact that the degree of reaction is dependent to some extent on variations in the host's