807 
THE VETERINARIAN, NOVEMBER 1, 1879. 
Ne quid falsi dicere audeat, ne quid veri non audeat.—C icero. 
THE EFFECT OF RAINFALL ON THE PREVALENCE OF 
PARASITIC DISEASES. • 
Last month we referred to the effect of the continued wet 
on the food of animals and the consequent want of tone in 
the systems of the creatures which have been sustained for 
mouths past on watery herbage. It was also suggested that, in¬ 
dependently of the want of quality or proof in the meat so pro¬ 
duced, the animals would naturally be predisposed to disease. 
There is one important class of diseases of animals 
to which a wet season is not merely a predisposing but an 
eminently exciting cause. We allude to those maladies 
which are due to the invasion of parasites, the germs of 
which find in the perpetually moist surface or constantly 
replenished pools a congenial habitat, where they pass 
through the changes which are preliminary to their residence 
in the bodies of the higher animals. 
Liver-flukes among sheep, and threadworms (strongyles) in 
the air-tubes of lambs and calves, have been unusually abun¬ 
dant during the past summer and autumn, and had it not been 
the case that the temperature has been lower than the average 
throughout there is very little doubt that the maladies which 
are produced by those parasites would have been far more 
serious than they have already been. Warmth as well as mois¬ 
ture is an essential condition for the development of parasitic 
(Terms, but heat without moisture is inimical to them, hence it 
is known that hot, dry summers afford the greatest security 
against parasitic diseases, except in those localities where 
the surface water is too abundant to be dissipated by the 
summer’s sun. 
It is frequently asked how it happens that in wet seasons 
liver-rot and husk in calves and lambs become prevalent in 
positions where, in dry seasons, they are never known, and 
in some cases on lands which, so far as anybody can prove, 
have never been infected with parasitic germs. The answer 
