8 FARMERS BULLETIN (13. 



DETECTING SCAB IN THE EARLY STAGES. 



The most certain diagnosis consists in demonstrating the parasite 

 {Psoroptes communis ovis) which alone causes the disease. To 

 obtain specimens of live mites one of two methods is usually em- 

 ployed ; first, lifting the mite from the surface of the skin with the 

 point of a knife blade, and second, taking scrapings of wool and 

 epidermis containing the mites and isolating the parasites from such 

 scrapings. To obtain mites with a knife blade, good light is neces- 

 sary. The wool around the affected area is suddenly parted with the 

 forefinger and thumb, and by the aid of a magnifying glass or even 

 with the naked eye the mites can often be seen moving rapidly away 





.A 



from the light. When they are thus found they can often be picked 

 up on the end of a knife blade. 



When scrapings are taken the outer edges of the infected areas 

 should be scraped with a blunt-edged knife. The mass of scrapings 

 is transferred to a smooth, black surface such as the brim of a black 

 hat or a piece of black paper. To make the mites active the tempera- 

 ture should be approximately the temperature of the body. Spread- 

 ing the scrapings in the bright, warm sun or near artificial heat will 

 usually cause the mites to become active, and they can be seen as 

 minute gray moving bodies against the dark background. They are 

 quite plainly visible under a low-power hand lens. 



When the mites are producing active irritation the surface of the 

 skin in the immediate vicinity of the lesion is greasy and appears 

 bright and glistening or white and glossy. Under such conditions 



