DISEASES OF THE SKIN AND SUB-TISSDES. 279 



animals, with a few observations on the dog-flea (pulex canis). 

 Scabies is a pestiferous disease, whether it aflects the horse, th« 

 ox, the sheep, swine, or poultry, inflicting a loss not easDy esti- 

 mated; he;jce the maxim of every intelligent farmer is, to avcid. 

 With him "prevention is better than cure," and, therefore, hia 

 grand desideratum is to guard against contagion. Sheep are, p-er- 

 liaps, more subject to it than any of the other animals, arising aa 

 much from the nature of their skins and coats as from the fecun- 

 dity of the acarus ovis, and the greater vicissitudes of the weather 

 to which they (the sheep) are exposed. Certain parts of the body 

 aie more liable to be affected than others; and so is an unhealthy 

 skin than a healthy one. Indeed, it has been said that an unheal- 

 thy skin will itself produce scabies (?), but this conclusion does 

 not apj^ear to be well founded ; for a disease dependent upon the 

 presence of living parasites can never arise spontaneously, but 

 must be effected by contagion, either by means of their eggs, or 

 the insect in some other stage of its existence. 



Now, from what has just been said, it will appear obvious that 

 cleanliness, a healthy skin and state of the body, and a separatloL 

 from foul animals and ground, are the means necessary to avoid 

 contagion. The truth of this will, perhaps, be better understood 

 if we first review the important distinctions which Mr. Simonda 

 makes between the habits of the acarus scabiei of the human bodv 

 and the acari of our domestic animals, the former burrowing in 

 the skin, but the latter living on its surface, clinging to the skin, 

 hair, or wool with their trumpet-shaped, vesicular-cushioned foet, 

 to prevent their being thrown off by the animal when shaking or 

 nibbling itself Hitherto distinctions of this kind have been over- 

 looked, ^vriters generally concluding that the acari of quadrupeds 

 l)urrowed in the skin like those of man, thus proving the little 

 use which had been made of the microscope in examining the 

 former, as it shows them to be incapable of living in the skin, 

 from the configuration of their bodies. Indeed, to have made 

 similar acari for naked skins as for those covered with hair, wool, 

 or feathers would have been an ovcrsiglit on the part of Nature; 

 while the fact that the acarus scabiei will not live on the horse, 

 nor awirus equi on man, or acarus ovis on the ox, or acarus bovis 

 on the sheep, and so on, proves that greater differencas than the 

 mere configuration of the animal structure exist, all pointing to 

 the above means as necessary, in every case, to avoid so great 9 



