CHAPTER II. 

 PHTHIRIASIS, 



The term phthiriasis is applied to infestation of the skin with Hce. 



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

 sites which Hve 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 Hamatopinus and Trichodectes. 



The HcematopiiiiLs forms have pointed heads, and are equipped for 



Fig. 245. — Hcsmatopinus eurystermts of 

 the ox, magnified 20 diameters. (After 

 Neumann.) 



Fig. 246. — Hcematopinus of the calf, 

 magnified 20 diameters. (After 

 Neumann.) 



penetrating the skin by suction. The Trichodectes have a large flat 

 head constructed for masticating. 



The ox harbours two forms of Hcematopmus and one of Trichodectes, 

 the Hcematopinus eurysternus and tenuirostrus, and the Trichodectes 

 scalaris. 



The sheep suffers from Trichodectes spherocephdlus and a Melophagiis, 



