Fig. 416.
Tyroglyphus. 1. Pediculus vulgaris × 50 diameters; 2. Acarus destructor under surface; 3. Sarcoptes scabici, Itch-insect, magnified 350 diameters; 4. Demodex folliculorum from the human skin in various stages of growth, from the egg upwards, magnified 400 diameters. (The small circles enclose the objects of the natural size.)
Fig. 417.—The Cheese Mite, Acarus domesticus, seen in its several stages of development.
Fig. 418.—Dermestes lardarius: larva, pupa, and imago. (Natural size.)
Birds suffer much from mites living parasitically upon them belonging to Sarcoptidæ; these likewise infest mankind, and give rise to a disease known as the itch (Fig. 416, No. 3). This malady and the irritation accompanying it are caused by the mite excavating tunnels under the skin. In these the eggs are laid and hatched, and the young then start burrowing on their own account; their burrows are traced as whitish lines on the surface of the skin.
[Fig. 416], No. 4, Demodex folliculorum, is another remarkable parasite found beneath the skin; this is usually obtained from a spot where the sebaceous follicles 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 pustule is seen be squeezed rather hard, the oily matter there accumulated will be forced out in a globular form. This minute mite is less than one-fiftieth of an inch in length; if it be laid on a glass slide, and a small quantity of glycerine added to cause the separation of the harder portions, the parasite in all probability will float out, and, by means of a fine-pointed pencil or brush, can be transferred to a clean slide and mounted in Canada balsam. An allied species is found in the skin of dogs suffering from mange.
