210 
The Aberystwyth Area 
other equally vague terms; but tor 18 out of the 77 flocks definite 
figures were given me, from which it appears that 1-64 % of the lambs 
and yearlings were affected; the usual being 1 to 1-5 % and the highest 
4 % (in one flock). 
C. Thirty flocks; affected 22, free 8. Two were but slightly in¬ 
fected, and out of the remaining 20, 12 furnished definite figures, working 
out at an average of 2-3 % of lambs and yearlings, the highest reported 
being 4-5 %. The percentage of flocks infected is 76-3. • 
The marked contrast between A on the one hand, and B and C on 
the other is at once apparent, and may be ascribed to one or more of 
three factors: 
(1) summering on the mountains, 
(2) wintering in the lowlands, 
(3) travelling along the roads. 
All the data for group C are not available, since in each case farms 
or sheep walks outside the Area are involved. In the case of lambs 
travelling into the Area in October for winter grazing the probability 
is that they were infected before they left their own farm or hill run. 
A certain number are generally too sick to travel back in the following 
April and remain, to die, on the lowland farms or fall out on the way. 
Some of these lambs come from considerable distances, Corris, Newbridge 
on Wye, Rhayader etc. in Radnorshire, many parts of Breconshire, and 
even Carmarthenshire; and are two to three days upon the road, being 
put for the night into certain fields regularly used for this purpose; the 
reverse process occurs six months later. Considerable opportunity 
exists in these cases of infection taking place en route. 
A few flocks, mostly in the northern part of the Survey Area “tack” 
lambs for the winter in the vicinities of Port Macloc, Criccieth and other 
places even further away. These lambs are sent by rail and not by 
road, yet Cfid occurs among the flocks. 
The best data are available for class B. In this instance the majority 
of lambs are born during March—April in the lowlands and are' moved 
to the mountains in April and May; hence they naturally graze but 
little before leaving the lowlands: or, they are born upon the lower 
lands of the hill sheep walks and do not go to the lowlands until autumn. 
I have compared the data for both these groups and they point con¬ 
vincingly to the sheep walk as the chief source of infection. Although 
the range there is wide, yet the sheep speaking generally do not wander 
so much as might be imagined, and keep,, very largely to their own 
