274 DISEASES OF THE SKIN. 



man attributed this predilection to the thinness of the skin, 

 and the circumstance derives additional evidence by com- 

 paring itch with mange. Hurtrel d^Arboval, however, 

 ascribes the partiality to adipose matter, and looseness of 

 the skin. 



Symptoms. — We seldom detect mange before it has made 

 considerable progress. There are but two ways in which its 

 presence is made known : — by the animal being observed 

 to rub itself, and the state of the skin ; which latter circum- 

 stance is not likely to be noticed until the hair begins to 

 fall off. The disease is an eruptive one. It commences in 

 the formation of minute pimples whose summits gradually 

 expand into vesicles, which burst and coalesce, thus forming 

 patches of incrustation, wherefrom the hair loosens at its 

 roots, and either falls or is rubbed off; leaving the places 

 bare, and the cuticle exposed, arid, and white ; a lifeless 

 state in which it desquamates in the form of scales and white 

 dust. Upon the hairless patches may be perceived small 

 red spots : these are owing to the crusts being rubbed off 

 the pustules ; the disturbance of the crusts is likely to cause 

 bleeding, producing little bloody scabs. The roots of the 

 hair appear to be secondarily affected, for the coat 

 does not come off until the disease has existed some 

 time : then the adherence of some hairs is often remarkable 

 enough. In inveterate mange the skin undergoes farther 

 changes in its structure, such as loss of elasticity, and corru- 

 gation into harsh, arid folds. 



The INTRINSIC Nature of mange is interesting rather for curiosity 

 than utility. It is dependent on the presence of animalculae — minute 

 insects named acari. On removing with a brush the scaly dust, and 

 examining it in the sun, may be distinguished little, organized, shining • 

 bodies moving about, which are the acari. In the horse, the insect is 

 large enough to be seen without the aid of a lens. After all, however, so 

 unimportant in pathology is the insect, that we rather side with Morgagni 

 in opinion, who, though he does not question the existence of the acari^ 

 doubts if all mangy pustules possess thenu" 



July, 1851. — Mr. Ernes sent me (in a letter) some acari to examine 

 that were taken from a mangy horse. We put them under the micro- 

 scope, and found that they somewhat resembled minute crabs, having 



