THE ITCH-MITE OF MAN. 



55 



eggs 0.14mm). This species has been found upon man, ape, 

 horse, sheep, lion, llama, ferret, and other animals. 



The itch-mite lives in self-made burrows just beneath the 

 epidermis or scurf-skin. These burrows (fig. 29), called by 

 physicians "acarian furrows," extend through the deeper 

 layers of the epidermis to and into the true skin. During the 

 existence of the mites in the burrows, which are similar to 

 the underground tunnels made by a mole, the mite moults 

 three times, w^ithout, however, greatly 

 changing in general appearance ex- 

 cept in size. The eggs, large in com- 

 parison to the size of the mother, are 

 elongate-oval, with a smooth skin. 

 From 20 to 24 eggs are said to be de- 

 posited at a time, and they hatch in 

 4 or 7 days. Such eggs, if kept in 

 moist surroundings, remain good from 

 three to four weeks. The mites, if re- 

 moved from the host, can also exist 

 for a long time if kept moist, but 

 die in four to six days in dry sur- 

 roundings. The female mite, as she 

 progresses in digging a burrow, lays 

 the eggs behind her, and soon dies. 

 These eggs can be seen in a regular 

 row in the burrow (fig. 29). 



Fig. 29. — Acarian fur- 

 row; a, freshly laid egg; b, 

 «ggs showing segmenta- 

 tion; c to d, eggs showing 

 embryo; e, empty egg- 

 shells; the black spots are 

 ■excrement. Greatly en- 

 larged. After Heller. 



We know the skin of the host is 

 constantly wearing off and as con- 

 stantly renewed by new growth from 

 beneath. This being the case the eggs 

 in the burrow will reach the surface just about in time to 

 hatch and to permit the young animal to escape. These bur- 

 rows are from one-twelfth to a quarter of an inch long and 

 possess a serpentine form. They can be detected below the 

 surface of the skin as a whitish dotted line, the dots corre- 

 sponding to the eggs. Over the entrance made by the mite 

 there is usually a little pimple on the skin containing a wa- 

 tery fluid. When we try to obtain the mite by puncturing 



