1920.] 



Diseases in Animals durinc; 1919. 



809 



between each dipping. An extension of this interval is 

 contrary to our knowledge of the life history and physical 

 properties of the parasite and its eggs. Several dipping agents 

 can be reasonably relied upon to kill the parasites of scab, 

 but the eggs are resistant to such agents, and they may 

 hatch out after one dipping, only to start the disease over 

 again. If, however, there are two dippings, and the interval 

 between is as above mentioned, the second dipping may be 

 expected to destroy the parasites hatched out after the first 

 dipping before they are ready to lay eggs for another brood. 



The single statutory dipping has been a hindrance to the 

 eradication of scab inasmuch as it has had the effect of hiding 

 the visible symptoms of the disease for long periods, giving 

 a sense of false security as regards sheep purchased. Such 

 sheep have only too often passed from the latent to the 

 visible stage, and have been the origin of outbreaks in the 

 flocks of others who have bought them, believing them to be 

 free from infection. Sheep bought at Perth, for example, 

 have caused serious outbreaks in the South of England. It 

 may surprise those who support a policy of single dipping 

 to learn that practically every outbreak of scab which has 

 occurred since the policy of single dipping was introduced as 

 a concession to the views of sheep owners, has arisen from 

 sheep which had been dipped once, or twice with a long interval, 

 during the previous six months. No policy which does not 

 involve double dipping can be regarded as an anti-scab 

 measure. This does not mean that it is necessary to subject 

 all the sheep in the country to double dipping in order to 

 eradicate sheep scab. Such a policy would defeat itself by 

 being excessive, since the areas in which no disease is known 

 are much in excess of those in which it is known or seriously 

 suspected of lurking. It does mean, however, that for pur- 

 poses of eradication, Sheep Scab must be rigorously attacked 

 in its lurking places, and that any measures which are based 

 upon one dipping, or multiple dippings^ with long intervals 

 are, as regards Sheep Scab, a waste of effort and money, and 

 are foredoomed to failure. 



In the circumstances it would seem advisable that the 

 Ministry should dissociate itself from measures against Sheep 

 Scab which have for their basis a single dipping. 



With regard to Parasitic Mange it is pointed out that owing 

 to the War the Parasitic IMange Order of 1"911 was suspended 

 in August, 1914. until March, 1915, and that it has been 



