618 SCABIES — SCAB— MANGE. 



these points, it may be remarked that the eggs may not hatch for 

 six or seven days ; the six- legged larvae may moult when three to 

 four days old, and become mature ; after pairing, a second moult 

 takes place, lasting four to five days ; a third moult follows imme- 

 diately, then eggs are laid and the adults die ; in some cases there 

 is a fourth moult, but apparently without any further production of 

 eggs. Accepting Gerlach's estimate of fifteen days as an average for 

 each generation of ten females and five males, in three months' time 

 the sixth generation would appear and consist of about 1,000,000 

 females and 500,000 males. 



Several practical lessons are to be drawn from these figures : Firstly, 

 it is seen that the parasites increase very rapidly, so that if scab is 

 discovered in a flock, the diseased sheep should immediately be iso- 

 lated ; secondly, if new sheep are placed in a flock, they should either 

 first be dipped, as a precautionary measure, or they should at least 

 be kept separate for several weeks to see whether scab develops ; 

 thirdly, since the chances for infection are very great, the entire flock 

 should be treated, even in case scab is found only in one or two 

 animals ; fourthly, as dipping is not certain to kill the eggs, the sheep 

 should be dipped a second time, the time being selected between the 

 moment of the hatching of eggs and the moment the next generation 

 of eggs is laid. As eggs may hatch between three and seven, possibly 

 ten or eleven days, and as fourteen to fifteen days are required for the 

 entire cycle, the second dipping should take place after the seventh 

 day, but before the fourteenth day; allowing for individual variation 

 and variation of conditions, the tenth, eleventh, or twelfth day will be 

 the best time to repeat the dipping. 



Symptoms. Psoroptic mange attacks the parts covered with wool, 

 so that attention is only drawn to the disease by some slight injury 

 to the fleece, which becomes rough, matted, brittle, and liable to fall. 



Scabies commences with intense pruritus. The animals scratch and 

 bite themselves, and tear away the fleece. These symptoms become 

 aggravated when the animals are hot, as, for instance, when travelling. 

 If the sheep have travelled through mud, the fleece becomes matted 

 on the neck, behind the shoulders, and at all points where they are 

 able to scratch themselves with the hind limbs. 



When a scabby sheep is touched at a diseased point, the animal 

 shows pleasure by nibbling and moving the head up and down. 



At an early stage, if the fleece is divided and the skin examined, 

 little papules may be discovered somewhat less in size than a lentil. 

 They are of a yellowish colour, and are distinctly visible against the 

 reddish colour of the skin. These papules are due to the attacks of 

 the psoroptes. 



