DIP MATERIAL 649 



lying ; and the eggs have been proved to retain their vitality 

 for years in a dry and equable climate, and to hatch out on 

 gaining access to a sheep. It is this wonderful vitality of the 

 egg which has in a great measure led to the belief in the 

 spontaneous-generation idea, 1 and which makes the stamping- 

 out process difficult But the chances of distribution by this 

 means are enormously reduced when outbreaks are promptly 

 dealt with and the sheep are not allowed at any period of the 

 year to become badly affected. The mixing of clean and 

 affected sheep, or their meeting on opposite sides of a wire 

 fence, is the fruitful source of contamination when sheep 

 suffering from scab travel on a public thoroughfare. Sheep 

 in poor condition, 2 or those suffering from constitutional 

 weakness or bad management, yield to the insidious attacks 

 of the parasite much more readily than robust animals in 

 good condition, although all sheep suffer in the end when 

 fully and freely exposed to contamination. Others again, 

 such as Welsh mountain sheep, yield more readily to treat- 

 ment than many of the Lowland breeds. These are not 

 features peculiar to this country, as in South Africa scabbed 

 sheep in the dry Karoo are well known to be more easily 

 dealt with than those on the moist grassy lands near the 

 coast, and long-wool sheep in the Argentine offer less 

 difficulty in treatment than Merinos. 



Dip Materials. 



The poisons present in all the common effective dips 

 resolve themselves into a limited number of well-known 

 chemical substances which, in wholesale quantities, can 

 be procured at very moderate prices. They are essentially 

 four arsenic, sulphur, decoctions of tobacco, and carbolic 

 acid. For 100 sheep, 10 Ibs. of hellebore (boiled for an 

 hour) and stavesacre are sometimes used with excellent 



1 Starlings and jackdaws, which settle on the backs of sheep in search 

 of the larger forms of ovine parasites, are capable of transmitting scab 

 from one flock to another located at considerable distances apart, and an 

 extensive sheep farmer has suggested to us that flies might also, as in 

 other cases of infection, carry the parasites from one sheep to another 

 and further complicate the question of the unexplained causes of 

 outbreaks. 



2 Some authorities say especially when beginning to thrive. 



