ACARUS DOMESTICUS. 637 



fully the parts surrounding each pustule, he will then see 

 a red line or spot communicating with it ; this part, and 

 not the pustule, must be probed with a fine-pointed instru- 

 ment ; the operator must not be disappointed by repeated 

 failures. . Dr. Bourguignon bestowed much time in 

 studying the habits of this troublesome parasite. To 

 arrive at a knowledge of its haunts he arranged his mi- 

 croscope so as to enable him to observe it under the skin 

 of the diseased person. The rays of light from a lamp or 

 candle must be carefully brought to a brilliant focus by 

 means of the condensing or bull's-eye lens upon the 

 chosen point of observation ; a Leiberkuhn should also be 

 attached to the object-glass. 



No. 4, fig. 290, Demodex folliculorum, is another re- 

 markable parasite found beneath the skin of man : it is 

 sometimes obtained from a spot where the sebaceous folli- 

 cles, or fat glands, are abundant ; such as the forehead, the 

 side of the nose, and the angles between the nose and 

 lip ; if the part where a little black spot or a pustide is 

 seen be squeezed rather hard, the oily matter there accu- 

 mulated will be forced out in a globular form ; if this be 

 laid on a glass slide, and a small quantity of oil added to 

 it, to cause the separation of the harder portions, the 

 parasite in all probability will float out ; after the addition 

 of more oil, it can then be taken away from the oily 

 matter by means of a fine-pointed sable pencil-brush, and 

 transferred to a clean slide ; when dry it should be im- 

 mersed in Canada balsam, covered over with thin glass, 

 and mounted in the usual way. 



The Cheese-mite, Acarus domesticus (fig. 290, ]S"o. 2), 

 has a peculiar elongation of its snout, forming strong, 

 cutting, dart-shaped mandibles, which it has the power of 

 advancing separately or together. The powder of old and 

 dry cheese almost entirely consists of mites and their eggs, 

 which are hatched in about eight days ; if deprived of 

 food, they have been seen to kill and eat each other. 

 Acari infest almost the whole of our dried articles of 

 food. Ac. passularum has two very long buccal bristles; it 

 lives upon dried figs, and other saccharine fruits. Ac. de- 

 structor has long black hairs ; it feeds upon the contents 

 of entomological cabinets, especially butterflies; Ac. p?'u- 



