GEOFFREY
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exception of a negative egg count on the day after the last of these three doses,
no lasting effect on the egg count was noted. No further doses were therefore
given. The egg counts remained at a mean of 100 for a further 14 days after
the last dose, when the egg counts were discontinued. The animal was
however, kept in the box with the Unmarked Lamb until 8-4-40. On 7-4-40
and 8-4-40 its egg count was 0 and 100 respectively.
The history of the Unmarked Lamb was similar. After the initial dose of
0.27 gramme per lb. body weight (24 grammes) its egg count dropped from a
mean of 3,850 e.p.g. to a mean of 550 e.p.g. It remained slightly higher than
that of the Marked Lamb. On 6-1-40, 57 days after the initial dose, an attempt
to remove its remaining worms was made by giving it in water as a drench
9 grammes of phenothiazine powder. Two days after this dose the egg count
had dropped from a mean of 500 e.p.g. to 0. The next day (9-1-40) it had
risen again to 50 e.p.g. and remained at this level till 15-1-40, when it was 200
e.p.g. On 17-1-40 it was 350 e.p.g. On 19-1-40 and 20-1-40 two successive
doses of 9 grammes each were given in the form of the 1 gramme tablets
in gelatine capsules. The day after the second of these doses the egg count
was 0 and it remained so until 25-1-40. On this date and on 26-1-40, two
further doses of 9 grammes of the same tablets were given and the egg count
remained at 0 until 31-4-40, when it was 100. On 31-1-40 and 1-2-40 and
2-2-40, three successive doses of 9 grammes each of the same tablets were given.
From 3-2-40 to 7-2-40 the egg count remained at 0, but was at 100 e.p.g. on
7-2-40. It remained at this level until 16-2-40 when the egg counts were dis-
continued until 8-4-40 when the count was 0 again, although this lamb had been
in the same box with the Marked Lamb, which still had an egg count of 50 to
100 e. p.g.
The undosed ewe had a mean egg count on the first three days of the experi-
ment of 1,350, 2,700 and 1,800 respectively, but by the fifth day it had fallen,
without dosing, to 600 and thereafter fluctuated between 400 and 800 e.p.g.
until 7-12-39, when it was killed off by mistake. It did not therefore provide a
very satisfactory control. The fall in its egg count without dosing is, however,
a point to be noted, because this frequently happens in all kinds of animals and
must be considered when the egg count is used as a criterion of the effect
of any anthelmintic.
The conclusion drawn from this experiment was that a dose of about 0 . 3
gramme per lb. body weight removed most of the worms of a light infes-
tation, but that a few remained, which it was difficult to remove with
phenothiazine, perhaps because the animals were confined in a box
and probably self-and cross-infestation were occurring all the time. Animals
in the field would be subject to much heavier infestations after dosing, so that
it would be even more difficult, if not impossible, to reduce their egg counts to
0 and to maintain it so. The reduction of the egg counts to 0 for three or four
days was not regarded as significant, because egg counts are notoriously fallible
as evidence of the degree of an infestation. In any event, the failure to pro-
duce a negative egg count over long periods may carry with it the advantage
that the retention of some worms by an animal helps to maintain its resistance
to further infestation. On the other hand, Gordon (1939) (Austral. Vet. J. 15.
118-120) has pointed out that in a sheep harbouring, say 8,000 Haemonchus