SHEEP SCAB. 5 



the .young mites after hatching to grow to maturity, mate, and de- 

 posit their eggs, it would ai:)pear that the hest time for the second 

 dipping is about 10 days after the first, as all the eggs will have 

 hatched, while practically none of the new generation of mites will 

 have developed sufficiently to deposit eggs. Practical experience 

 has shown that the second dipping may be delayed until the four- 

 teenth day without unfavorably affecting the results of the treat- 

 ment, but wherever possible it is preferable to follow the 10-day rule. 



VITALITY OF SCAB MITES. 



The species of mite which causes common sheep scab is unable to 

 propagate itself except on the bodies of sheep, its natural host. Mites 

 of this species, however, Avhen removed from the host, are able to live 

 for some time, the period of survival varying under different con- 

 ditions. 



From a practical point of view and because of the spread of infec- 

 tion from diseased to healthy sheep through the medium of stables, 

 pastures, etc., and the fact that the mites or their eggs, scattered by 

 diseased sheep, may survive until picked up by healthy sheep, this 

 (question of the leng-th of time that mites or their eggs may retain 

 their vitality when away from the host is obviously an important 

 one. Various data which have been collected relative to this sub- 

 ject show that mites removed from the body will commonly live 

 from 2 to 3 weeks, and cases have been recorded of their survival 

 for as long as 2 months. It appears certain that under natural con- 

 ditions they sometimes live much longer. 



A dry atmosphere is very unfavorable to their existence away from 

 their host. Other things being equal, scab mites will live longer off 

 the body in a cool, moist atmosphere than in a warm, dry one. 



Owing to varying conditions which may affect the longevity of 

 mites and the vitality of their eggs wdien away from their natural 

 host, it is impossible to make definite statements as to the length of 

 time infection of pastures and buildings may persist after sheep have 

 been removed from them. It is fairly safe to assume, however, that 

 a month or two will suffice to free open pasture from infection, but 

 that buildings, pens, bed grounds, etc., will not be safe even after a 

 year or more; consequently these latter places, when they have been 

 occupied by infested sheep, should be abandoned, destroyed by burn- 

 ing, or thoroughly cleaned and disinfected before they are used for 

 clean sheep. 



SYMPTOMS OF SCAB. 



When the scab mite finds lodgment on a sheep it pricks the tender 

 skin to obtain food, and in so doing probably introduces a poisonous 

 saliva into the wound. A slight inflammation is caused, made man- 



