52 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ I, I
on fluke-infested farms during the dry season (as the products of burnt rushes are detrimental to the
growth of those snails which live in shallow water) ; complete drying up of pools for short periods ;
and the use of lime and sulphate of copper for the destruction of the snails.
Hornby (1921) has noted the susceptibility of snails and their eggs to desiccation, whilst Melek
(1927) regards the draining of " all swampy places " as the first essential in combating the snail popu-
lation in a locality. Melek also records having found both salt and lime as being capable of destroying
snails, but he advises the use of copper sulphate (in a solution of one in a million) as being "more
effective, cheaper, and more easily applied".
(c) Work in Wales.
Walton (1923) tested the relative killing power of ammonium sulphate and copper sulphate,
under field conditions, for the two common species of snails in Wales, namely, Limnæa truncatula
and L.peregra, and as the result of his investigations he recommended the latter chemical as being,
on the whole, more effective, provided the "usual precautions" were taken " as to avoidance of
stocking treated ground until after heavy rain, and the exercise of care in treating flowing streams
that may be used for watering stock, or may affect fishing water, etc." Walton cites an instance in
which several ditches cleared of snails by the use of bluestone dusts 18 to 24 months previously were
re-examined and found free of snails. He also quotes an example in which complete eradication of
snails was effected by ploughing and putting under oats several large damp grass fields which had
previously swarmed with L. truncatula (and had caused very heavy losses in 1920-21), thus
indicating a method of treatment of value for such land.
Daubney (1924) too refers to valuable results having been obtained from the use of copper
sulphate in combating L. truncatula. The plan adopted by him for application under field condi-
tions was to spray infested pastures with a one per cent. solution of copper sulphate and to dress
ditches with powdered copper sulphate. In illustration of the benefit derived from this method of
treatment Daubney observes : " Such treatment has been efficacious in removing snails from heavily
infested lands, and after two years one farmer reports the complete absence of fluke in the sheep killed
for food. It was stated that in 40 years' experience on this particular farm never before had a whole
season elapsed without the occurrence of some flukes in the sheep killed." The effect of one appli-
cation of copper sulphate was observed to last for at least two and a half years. Daubney, however,
emphasizes the fact that the application of copper sulphate per se is not calculated to confer lasting
benefit unless it is accompanied by efficient drainage of the land, " including the prevention of
inundations and the improvement of ditches ", and he cites instructive examples of the permanent
value of drainage works in this respect in badly infected localities.
Perhaps the most extensive work yet conducted, under field conditions, upon the use of copper
sulphate in destroying the molluscan hosts of trematodes was that carried out by Walton, in Wales,
in 1925. His conclusions are of sufficient practical importance to bear quotation at some length.
Three methods of employment of the salt were adopted by him, depending upon the nature of the
land which it was sought to rid of snails :—
1. Spray. Solutions of 2, 1 and ½ per cent. were all equally effective under varied field condi-
tions. The method is especially suitable on damp land. Where the land is water-logged, there is a
possibility of a ½ per cent. solution becoming too dilute to be effective, and under such conditions, it
would probably be advisable to use the higher strengths. On the other hand, snails may remain
alive on land that has become partially dried and it is then essential that the surface shall be tho-
roughly wetted. The amount of fluid required to do this will obviously depend upon the degree of
moisture already present in the land. In one plot (54 sq. yds.), where the land was damp below
heavy herbage, the amount used worked out at 137 gallons per acre.