PAEASITES 435 



topinus and one Trichodectes. The sheep has one Tricho- 

 dectes. The pig has one Htematopinus, which is the largest 

 known louse. The dog has a Trichodectes which is inter- 

 esting as being the intermediate host of a tapeworm, viz., 

 the T. cucwnerina. 



Lice in horses are an indication of neglect, and are 

 certainly never found where good stable management is 

 practised. The disease caused by them is easily cured by 

 clipping and thoroughly dressing with any of the known 

 remedies, of which stavesacre is perhaps the most common. 

 It is a practical point to bear in mind that the insect is 

 killed easier than the egg, so that the treatment should be 

 repeated after a few days, in case any eggs have hatched 

 out. 



PulicidcB or Fleas are only of interest as possible carriers 

 of disease. The Trypanosoma Leicisi of rats can be carried 

 by them, and the flea can also act as the intermediate 

 host of certain other parasites. 



Worms or Helminths are a frequent source of disease in 

 the lower animals, in some cases causing widespread 

 havoc, as in ' fluke disease ' and verminous bronchitis, in 

 others causing serious local loss, especially where the 

 stomach or intestines are attacked. There is hardly an 

 internal organ of the body which is not liable to be affected 

 by parasites, but it is only in those cases where the disease 

 is widespread that any serious attention is paid to the 

 matter. 



Our knowledge of the life-history of parasites is very 

 incomplete. Some, like the liver fluke and many of the 

 tapeworms, are well understood, but the origin and history 

 of the majority are unknown. 



Following the course previously adopted, we will only 

 examine in detail those parasites which produce widespread 

 or serious disease, the existence of the others being simply 

 noted. 



The Cestodes as a rule pass their cycle of existence 

 through two hosts. The second host may vary from a 

 warm blooded animal to a flea. It is only a knowledge of 



28—2 

 Digitized by Microsoft® 



