CHAPTER II. 

 PHTHIRIASIS. 



The term plithiriasis is applied to infestation of the sldn with lice. 



Causation. These diseases are due to the presence of various para- 

 sites which live by destroying the epidermic scales, or by piercing the 

 superficial layers of the skin. They are of a greyish-yellow colour, and 

 belong to the genera Hcematopinus and Tricliodrctes. 



The Hfematopinus forms have pointed heads, and are equipped for 



Fig. 245. — Hceniatoinnns curysternus of 

 the ox, magnified 20 diameters. (After 

 Neumami.) 



Fig. 246. — Hcematojnnus of the calf, 

 magnified 20 diameters. (After 

 Neumann.) 



.penetrating the sldn by suction. The Trichodectcs have a large fiat 

 head constructed for masticating. 



The ox harbours two forms of ILematojnnus and one of Trkhodectes, 

 the Hfematopinus envy stc runs and tenuirostnis, and the Trkhodectes 

 scalaris. 



The sheep suffers from Trkhodectes spherocephalus and a Melophagits, 



