330 THE MICROSCOPE. 



by repeated failures. As it is often very difficult to detect the haunts 

 of the insect, an eye-magnifier will greatly assist. 



Dr. Bourguignon has of late bestowed much time in studying the 

 habits of this troublesome parasite. To arrive at this knowledge, the 

 Doctor had recourse to a peculiar kind of movable microscope, which 

 enabled him to observe it under the skin of the diseased person. The 

 microscope is composed of the frame of an ordinary instrument, the 

 optical and essential parts of which have been raised from the socket 

 that supported it, and articulated to a movable knee at the extremity 

 of a lever. The rays of light from a lamp or candle are brought to a 

 brilliant focus by means of the condensing or bull's-eye lens ; which 

 focus is directed upon the chosen point of observation. 



He then saw that the feet were armed with suckers, which enabled 

 it to fasten itself in the furrows under the skin, aided by the small 

 bristles ; and being likewise covered by the same in various parts of 

 the body, it more firmly fixes itself there ; and with its terrible man- 

 dibles it accomplishes its destructive mission. It has no eyes j but in 

 the moment of danger it quickly draws in its head and feet, somewhat 

 resembling the tortoise ; its march is precisely that of the tortoise. It 

 usually lays sixteen eggs, which are carefully deposited in furrows un- 

 der the skin, and ranged in pairs ; these are hatched in about ten 

 days. 



No. 4, Plate XL, Demodex folliculorum, is another very remarkable 

 parasite found beneath the skin of man : it may be obtained from a 

 spot where the sebaceous follicles, or fat glands, are very abundant ; 

 such as the forehead, the side of the nose, and the angles between the 

 nose and lip j if the part where a little black spot or a pustule is seen 

 be squeezed rather hard, the oily matter accumulated will be forced out 

 in the globular form and various stages of growth, as represented in the 

 drawing ; if this be laid on a glass-slide, and a small quantity of oil be 

 added to it, so as to separate the harder portions, the little insect in all 

 probability will be floated out j after the addition of more oil, it may 

 be taken away from the oily matter by means of a fine- pointed sable 

 pencil-brush, and transferred to a clean slide, where it may be covered 

 over with thin glass, and mounted in the usual way. 



The Cheese-mile, Acarus domesticus (Plate XI. No. 2), has a peculiar 

 elongation of its snout, forming strong, cutting, dart-shaped mandibles, 

 which can be advanced separately or together. Their legs are brown. All 

 indeed present a great diversity of form, size, and colour ; and in the 

 cheese-mite we observe the peculiar adaptation of form and apparatus ne- 

 cessary for cutting its way into or through the food on which it is destined 



