GEOFFREY
LAPAGE
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symposium that phenothiazine, in amounts far too small to have any anthel-
mintic action in a host animal, will inhibit the development of eggs and early
larvae, although they do not affect the infective larvae. Such in vitro observa-
tions suggest a direct action of the drug. On the other hand, there is evidence
which suggests that the action of phenothiazine is more pronounced in rumi-
nant hosts, in which the drug has to pass through the rumen and other oesopha-
geal chambers of these animals, than it is in omnivorous hosts such as the pig
and the dog. It is possible that the intestinal contents of ruminants allow
the drug freer access to the nematodes than the pastier faeces of omnivora do,
but other factors probably operate as well. Swanson, Harwood and Connelly
(1940) (J. Amer. vet. med. Ass. 96. 333-338) found that phenothiazine was as
effective as oil of chenopodium for the removal of ascarids from mature pigs
and suggest that the ascaricidal principle of phenothiazine may be " activated
by the substances excreted by those worms." They thought it was more
effective when the infestations were heavy than when they were lighter. On
the other hand, Singer and Baker (1940) (Cornell Vet. 30. 375-382) found that
phenothiazine was more effective against lighter nematode infestations of sheep
than against heavier ones. Observations like these do, nevertheless, justify
the question, which is also raised by other points in the literature : Is pheno-
thiazine inactive as an anthelmintic until it is chemically changed in the gut, so
that its action is greater on species living in the lower part of the alimentary
canal ? There is urgent need for the investigation of this and collateral ques-
tions. Associated with them is the problem of why it is necessary, as all
workers agree that it is, to give so much phenothiazine, in order to produce an
adequate anthelmintic effect, that a great deal of it is passed out again in the
faeces apparently unchanged. This is a waste that might be avoided if we
knew how phenothiazine acts on a nematode ; we might then be able to use a
modified form of it, or a derivative of it, which would be more potent and per-
haps effective for all nematodes.
TECHNIQUE.—Differential worm counts were made by Taylor's technique
(1934) (Vet. Rec. 14. 474-475).
Egg counts were done by taking 3 g rammes of faeces from the animal,
either with the finger, or as they were passed, and emulsifying these in 45 c. c.
water ; 0 15 c. c. of this emulsion was then taken with a pipette and the eggs in
this amount counted. Multiplication by 100 gave the number of eggs per
gramme.
Wherever possible two counts, made by different observers (Lapage and
Bowman), were made from different portions of each sample of faeces and the
average of these was taken. Frequently these two counts differed widely.
Sometimes one was negative, while the others showed as many as 700 e.p.g. or
there were variations as wide as 7,500 and 200 e.p.g. in different portions
of the same sample of faeces. It was evident, therefore, that the average of
the two counts did not accurately represent the egg content of the faecal
samples, but this kind of error is common to all the egg counts made and will
not surprise helminthologists. In some experiments composite egg counts of
mixed samples from individual animals were made, because it was not possible
to do egg counts on each individual animal. Some of the disadvantages of
composite egg counts are discussed below.