THE SCAB. 227 



the time that elapses after the infection, before the disease appears. About the 

 twelfth day. it is stated by Youatt, the pustules begin to appear, and the rubbing of 

 the animals shows the irritation has commenced. In four days more the pustules 

 break, and the matter escaping forms the crust. 



After it was found that the itch in the human race was caused by an insect, a 

 species of acarus, it was supposed that similar cutaneous diseases might arise from 

 the same source. M. Waltz, a German, was the first to establish this point and filly 

 investigate its cliaracter; and numerous subsequent examinations have proven the 

 correctness of his opinion. He found that the scab, like the itch, mange, &c., is 

 caused by animalculce ; that the irritation caused by his burrowing in the skin forma 

 the pustule, and that when this breaks, the acarus leaves his habitation, and travels 

 to another part of the skin, and thus extends the disease, or it may he left on the 

 rubbing post, or the wool of an animal coming in contact. When one of thfise acari 

 is placed on the wool of a sound animal, they quickly travel to its roots, where the 

 place of burying themselves is shown by a minute red point. About the sixteenth 

 day the pimple or pustule breaks, and if the acari is a female, it appears with a mul- 

 titude of young. Tliese immediately set to work on the skin, bury themselves, and 

 propagate, until the poor animal is irritated to death, or becomes encrusted with 

 scab. M. Waltz satisfactorily traced the parasite through all its changes, and by 

 experiments discovered all its modes of action and method of infection. He found 

 that when the male acari was placed on a sheep, it burrowed, the pustule was formed, 

 but the itching and scab soon disappeared without the employment of amy remedy. 

 Such was not the case where the female acari was placed on the .sound skin ; as with 

 the breaking of the pustule, from eight to fifteen little ones made their appearance. 

 M. Waltz found that the young acari kept in a dry place dried and crumbled to dust, 

 but when old, that it would retain its life through the whole winter, thus proving 

 the necessity of not relying on the season for their destruction, but on preparations 

 of active medicine when the disease shows itself. Of the origin of these insects we 

 of course can know nothing ; it is enough that we are certain when they make their 

 appearance, they can be mot and destroyed. 



Various remedies have been recommended for the cure of the scab; but although 

 the sheep acarus is very different in form, size, and colours from the human acarus, 

 the application that will destroy one will prove fatal to the other. The remedy is 

 the destruction of the acarus. 



A strong decoction of tobacco, of hellebore, or a solution of arsenic, will cure; 

 but the difficulty with washes is, that the burrowed insect sometimes goes untouched, 

 and unless the washing is repeated, some are apt to escape, and the disease is con- 

 tinued. Owing to this, it lias generally been deemed a safe and more expeditious 

 mode to use the mercurial ointment. When used too strong it will salivate lambs 

 or ewes. Where the cases are very bad, the ointment may consist of ■one part of 

 mercurial ointment or unguentum, with three parts lard \, hut for orrfj'nary cases of 

 scab, one part of the mercurial ointment to five of lard »<'ill be suffiriently powerful. 

 The wool should be separated, a small quantity pl?<^d on the skin, and carefully 

 rubbed in. The extent of the application and the^quantiO' nsed will depend on the 

 spread of the disease, from half an ounce to two^unotfs being demanded. A decoc- 

 tion of tobacco or hellebore will cure, but as be^re remarked it may be necessary to 

 repeat the washing. Arsenical applications/are ^jTectual, ftut dangerous, unless 

 great care is used. Where an animal has be»» warned, or oiitment applied, infection 

 is generally iirevenled; hut whenever the /ab rppears. and is supposed to be cured, 

 examinations at the end of every few ^ys -hould take place, particularly if any 



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