166 HEALTH AND DISEASE 



as experience proves that the arms are the parts most likely to be 

 attacked. 



PARASITES OF THE SKIN DERIVED FROM THE ANIMAL 



KINGDOM 



I 



The skin of the horse is infested by several varieties of parasites, 



which occasion disease of the structures, attended with itching, and in 

 some cases with considerable eruption. The two most common affections 

 are known by the terms phthiriasis, when lice are present, and acariasis, 

 when different kinds of acari invade the skin. The latter are the cause of 

 several forms of mange. 



Phthiriasis (Lousiness). Lice which infest the skin of the horse are 

 of two kinds: one which, by its sharp-pointed mouth, is able to puncture 

 the skin and live on the blood, hence called Hamatopinus, and another 

 the head and mouth of which are not adapted for puncturing the skin; this 

 variety feeds on the loosened cuticle and clings to the hair, hence the 

 name, Trichodectes, which is given to it. The two varieties are commonly 

 found together. In very young animals lice are frequently extremely 

 abundant, and by the constant irritation which they produce they prevent 

 the animal from feeding or resting in any comfort. It is consequently 

 important to employ some dressing which will have the effect of killing the 

 parasites. Various agents are in favour for this purpose; the most simple 

 is any kind of fat oil which will destroy the lice by stopping their breath- 

 ing pores, as train-oil and linseed-oil. Mercurial ointment is a very effec- 

 tive remedy, but it is also very dangerous. Tobacco water, made by boiling 

 an ounce of tobacco in a quart of water, is also a very good dressing, or, 

 instead, a solution of carbolic acid 1 part to 50 parts of soft soap and 

 water may be used. 



In consequence of the invariable presence of numerous eggs on the skin, 

 which will in all probability escape the action of the dressing, it is neces- 

 sary to repeat it in a week. Afterwards the animal must be examined 

 occasionally in order to ascertain if any more parasites are present. The 

 illustrations in Plate XXXVI, figs. 1 and 2 show the different varieties of 

 lice found on the skin of the horse. 



Acariasis (Mange). The parasites which belong to this division are 

 the different varieties of ticks and mange-mites. The presence of ticks on 

 the skin may be looked upon as an accidental circumstance, from which the 

 horse in its state of domestication is comparatively exempt. The same, 

 however, cannot be said of the invasion of the mange-mites, two varieties 

 of which are commonly found in the horse, one (Psoroptes) the cause of 



