348 



Sheep-Scab. 



crusts or scabs on the surface of the skin, and if a small por 

 tion of the crust, after being softened in a mixture composed 

 of glycerine and a solution of potash or soda, is teased out and 

 placed upon a slide, there will be found, in confirmed cases of 

 scab, whole acari, portions of the detached legs, and ova 

 mixed up with the fibres of the wool and fatty matter. 



It has been stated that the parasites of Sheep-Scab may be 

 easily identified by the naked eye, and there are some whose 

 experience enables them to easily do so ; but now that the 

 decisions of the Veterinary Inspectors of Local Authorities in 

 Great Britain are followed by serious consequences to the 

 owners if their sheep are certified to be affected with scab, it 

 is most important that no errors should be made in diagnosis. 

 It therefore becomes necessary that all enquiries into 

 reported outbreaks should be conducted on the above lines, 

 because, unless the particular acarus or some of the ova can 

 be discovered, the disease cannot properly be declared to be 

 present. 



Since the life history of the Sheep-Scab parasite has a 

 very important practical bearing upon that part of the Sheep- 

 Scab Order of 1898 which deals with the dipping of sheep, 

 it should be explained that the mature female after having 

 laid from 15 to 24 eggs dies, and the eggs are hatched in 

 about seven days, the young parasites becoming sexually 

 mature in about eight days, and another generation of eggs 

 being laid 14 or 15 days after the first. Effective dipping with 

 a suitable dip kills the acari, but may not destroy the vitality 

 of the ova 



It will thus be seen that not only do the acari rapidly mul- 

 tiply, but that it is necessary, if the disease is to be completely 

 eradicated from the flock, that the sheep should be dipped a 

 second time not later than the 14th day; for whilst the first 

 dipping might have killed all the acari, their ova may not 

 have been destroyed, and hence a second dipping becomes 

 necessary to kill the produce of these ova. 



There is another parasite which is frequently to be found in 

 the wool of sheep, viz., the common tick, or Melophagus ovinus, 

 represented in Figure 2 . 



It will be observed that this creature differs very materially 



