270
Anthelmintic Action of Phenothiazine
is mixed in the feed and the pigs are allowed to take it as they will, there is
danger that some will get too much and will suffer accordingly.
Larger doses will in the near future be given to pigs individually and the
results will be compared with those of Swanson, Harwood and Connelly
(1940) (J. Amer. vet. med. Ass. 96, 333-338), who gave up to 1 gramme per lb.
body weight to older pigs without toxic effects. Meanwhile, it is probably
wise to give phenothiazine to young pigs with great care. The Ascaris
burden of the pigs described above was not removed, nor much influenced,
by this dose of phenothiazine. The reason for this is not clear.
SUMMARY
(1) Two lambs weighing 74 lb. and 89 lb. were given 0.3 gramme and 0.27
gramme per lb. body weight respectively of phenothiazine in the form of
tablets. Three days after the dose the egg count had fallen, in the one case,
from 7.400 e.p.g. to 200 e.p.g. and, in the other, from 3,850 to 550 e.p.g.,
these egg counts being the mean of two counts done by different observers on
different portions of the same sample of faeces. The egg counts of both lambs,
which were kept in a box together, remained round about this figure for rather
longer than five months. Attempts to reduce the egg count to 0 and to main-
tain it at 0 by giving further doses of phenothiazine were not successful.
It is never desirable to remove all the nematodes from any animal because
this procedure will lower or remove the host's resistance to the infestation.
(2) Comparisons of the effect of phenothiazine, copper sulphate and copper
sulphate and nicotine on nematode infestations of ewes and lambs in the field
indicated that small doses (about 0.1 gramme per lb. body weight) of pheno-
thiazine lowered the egg counts more effectively than did either of the other
two anthelmintics and tended to maintain them more effectively at a lower
level. In three experiments 157 ewes and lambs were weighed every ten days
for a period of 30 days after doses of about 0.1 gramme per lb. body weight of
phenothiazine. The results indicated that, even when these small doses are
given, the weight increase of animals given phenothiazine is significantly
greater at the end of 30 days than that of animals given normal therapeutic
doses of copper sulphate or copper sulphate and nicotine, although, during the
first 20 days or so, the animals given these two latter anthelmintics appear to
put on slightly more weight. The egg counts of the animals given pheno-
thiazine were reduced more effectively than those given the other two anthel-
mintics and remained low. It is thus possible that phenothiazine has a more
lasting anthelmintic effect than copper sulphate and copper sulphate and nico-
tine, perhaps because it prevents the development of a second generation of
worms picked up from the pasture. Further experiments on this question are
in progress.
It is unlikely that a copper deficiency in the animals used contributed in
any way to these results, because there was no evidence of this and swayback
had never been reported from the district in which the animals used were bred.
(3) No toxic effects were shown by any of the sheep treated with these
doses of phenothiazine. It was not expected that the small doses used would
have any toxic effects,