236 PAEASITIC DISEASES OE THE SKIN. 



being necessary that they become deposited on the skin of the 

 sheep for them to develop into live and aggressive parasites. 



Gerlach, the German authority mentioned previously, com- 

 puted that in three months time a single female would be re- 

 sponsible for the existence of 1,500,000 progeny, as is shown in 

 the following table : 



First generation after 15 days produces. . . 

 Second generation after 30 days produces . 

 Third generation after 45 days produces . . 

 Fourth generation after 60 days produces . 

 Fifth generation after 75 days produces. . 

 Sixth generation after 90 days produces. . 



Unless the affected sheep is submitted to proper treatment 

 to destroy these pests they will increase indefinitely in numbers 

 until death to the patient ensues. The form of scabies com- 

 monly affecting the sheep in the United States from the Atlantic 

 seaboard to the Pacific Ocean is that caused by the psoroptes 

 communis, which attacks the parts of the sheep covered by the 

 lieavy fieece, causing the animal to rub and pull the fleece, so 

 effecting a shrinkage in the wool clip, which, when the large num- 

 ber of affected animals are taken into account, will be found to 

 annually mount up to millions of dollars, all of which could be 

 prevented by intelligently carrying out the Federal and State 

 regulations governing the same, subjecting all affected animals to 

 a rigid quarantine and effective treatment, and heavily punish- 

 ing the owner of a lot of infected sheep if he should wittingly 

 allow them to run at large. 



The common scab attacks the backs, flanks, sides, shoulders, 

 necks, bellies, and rumps of the sheep, the spot infected appear- 

 ing ragged, the sheep frequently biting the part as if it was try- 

 ing to tear the wool, or striking the spot with a hind foot; in 



