CLASSIFICATION OF ANIMAL PREPARATIONS. 421 



gauze ; in a few days or weeks numbers of insects will escape 

 from the gall, from a single oak-apple hundreds have been 

 known to make their appearance, and, perhaps, only one in 

 every six will exhibit beautiful colours, the others being 

 black, these may be rejected, as they exhibit no remarkable 

 structure. The colom'ed flies from gaUs of the following 

 trees may be procured very readily, and are amongst the most 

 beautiful of their kind : — 



Another tribe of minute insects is known by the name of 

 Acari, of these the cheese-mite, with its eight legs, is the 

 most familiar example ; generally speaking, these burrow into 

 the soft parts, and are only occasionally found on the surface. 

 One species, A. scabiei, is peculiar to the human subject, and 

 others to particular animals. With the Acari may be noticed 

 another parasite occurring in the sebaceous follicles, that in 

 man being called the Entozoon folliculorum. The subjoined 

 list wiU give the names of a few specimens of both kinds : — 



Aoarus autumnalis (Harvest-bug), Entozoon folKculorum (Man), 



domesticus (Cheese-mite), (Horse), 



scabiei (Itch-insect), (Dog). 



Method of obtaining the Acarus scabiei or Itch-insect. — 

 Many persons having so often failed in procuring the Acari 

 from the disease called itch, and those from the little black 

 spots about the face, termed acne, have been led to doubt the 

 existence of these minute creatures, on which account it has 

 been deemed necessary to give a few hints how they may be 

 best obtained. In the case of the itch-insect, Acarus scabiei, 

 the operator must examine carefully the parts surrounding 

 each pustule, and he wiU generally find in the early stage of 

 the disease a red spot or line communicating with it; this 

 part, and not the pustule, must be probed with a pointed 

 instrument, and the insect, if present, turned out of its 

 lurking-place; the operator must not be disappointed by 



