lU i ON ANIMAL PAEASITES. 



cause of the contagious skin disease of that name. The parasites 

 burrow under the skin and live on serosity, the effusion of which 

 is produced by the irritation which they excite. They are found 

 not on man alone, but on the sheep, dog, ox, horse, pig, cat, and 

 rabbit. Any animal may be the bearer of contagion between 

 other two, but it is essential for the development of a real scabies 

 on any animal that the insect should be proper to that animal. 

 For example, the parasite which lives on the dog does not live on 

 the sheep, and the parasite of the sheep will not contaminate 

 man. Thus, while the " itch " in man is caused by Sarcopiis 

 scabiei, the " scab " in the sheep is occasioned by Dermatodectes 

 ovis; and the " mange " in horses by Dermatodectes equi, in the ox 

 by Dermatodectes hovis, in the pig by Sarcoptis suis, and in the 

 dog by Sarcoptis canis. A smaller species, the Sarcoptis cati, pro - 

 duces the " mange " on the cat and the rabbit. 



3. Ticks. 



The ticks {Txodida)) are another family of the Acarina. 

 As many as six British species have been described ; but those 

 principally met with are the "dog-tick" {Ixodes ricinus), and 

 the "ked" or "sheep-tick" (Melophagus ovinus). The Ixodes rici- 

 nus is the true sheep-tick, and is commonly believed to give rise to 

 the disease amongst sheep known as " louping-ill," but it requires 

 to be proved. The tick breeds in the grass, and attaches itself to 

 both the sheep and the dog, and even the ox, when it gets an 

 opportunity, for the purpose of sucking their blood. The Melo- 

 piliagus ovinus, on the other hand, breeds upon the sheep, and the 

 name " ked " or " sheep-louse " is more appropriate to it than that 

 of " tick ; " but it is very often confounded with Ixodes ricinus, 

 although the two are totally different, as every one knows who 

 has once seen them. The " ked " is to be found more or less in 

 every flock, and if the sheep are not dipped at least once after 

 shearing, the keds become very numerous during winter, and by 

 the irritation which they excite, cause a great loss of wool, from 

 the sheep tearing the fleece with its teeth or rubbing against the 

 fences, not to mention the loss which accrues, by the animal itself 

 not thriving when in that state of torment. Both the ked and 

 the true tick are, however, easily destroyed and banished, or at 

 least kept under, by any of the sheep dips that are now in use. 



4. Lice. 



These parasites pass through no metamorphosis, and their mul- 

 tiplication is extremely rapid. Most, if not all, mammals are 

 infested by lice, each having generally its own peculiar species, 

 and sometimes, as in the case of man, two or three. The Pediculi, 

 or blood-suckers, of the class Anoplura, are those partial to man. 



