422 MANIPULATION. 



repeated failures, as, in the best marked cases, it is often diffi- 

 cult to detect the haunts of the creature ; when found, it may 

 be mounted in some of the preservative fluids — the glycerine, 

 perhaps, will answer the best. 



To obtain the Entozoon folliculorum, it is necessary to 

 choose some spot where the sebaceous follicles are very 

 abundant — the forehead, the nose, and the angles between 

 the nose and lips, being the regions that should be selected ; 

 if a part where a little black spot or pustule is seen, be 

 squeezed rather hard, the sebaceous or oily matter accumu- 

 lated unnaturally will be forced out ; if this be laid on a slide, 

 and a small quantity of oU added to it, so as to separate 

 the harder portions, the insects, in all probability, will be 

 floated out; after the addition of more oil, they may be 

 taken away from the sebaceous matter by means of a fine- 

 pointed sable pencil-brush, and transferred to a clean slide, 

 where they may be covered over with thin glass, and 

 mounted in the usual manner. The Entozoa are more 

 abundant in the skin of some persons than of others, but there 

 is rarely an instance where many black spots are seen about 

 the face or forehead from which they may not be obtained 

 after a careful search. 



Another species of Acarus, termed the A. autumnalis, or 

 harvest-bug, is very common in the autumn; these insects 

 crawl on the skin, and insinuate themselves into it at the 

 roots of the hairs, where they occasion a very painful 

 irritation; if these parts be examined, a number of minute 

 red spots will be seen, from each of which a reddish acarus 

 of small size may be dislodged by means of a needle or other 

 sharp-pointed instrument; this can be best seen in fluid, but 

 the structure of the darker kinds may even be satisfactorily 

 made out when mounted in Canada balsam. 



Another Acarus, and one which for very many years has 

 been the great source of delight to young observers, is the 

 A. domesticus, or cheese-mite ; this may be well shown either 

 as an opaque or a transparent object. As mites can be so 

 readily met with alive, it is hardly necessary to mount a 



