WITH reference to the disease existing amongst the carp at the Château de Montigny, and its presumed connection with “the first days of spring,” and the animosity of the toad for the carp, permit me to take up the cudgels, not for the early spring but for the poor maligned toad, which like other possessors of jewelled heads has already but too many enemies. On two occasions I have noticed the curious train of symptoms detailed by M. Duchemin, commencing with blindness, and ending in death. One occurred in Norway, and the trout and grayling were the only fish affected; the other in Lord Bathurst's park in this town, when the pike only were attacked whilst the perch and tench escaped. In both these instances I instituted a series of experiments to ascertain the probable cause of death. No intestinal worms were discoverable, nor did any of the tissues appear congested or otherwise diseased, with the exception of the eyes, in which the cornea became opaque and friable so that on very slight pressure the crystalline lens escaped. The long duration of this blindness before death supervened, rendered it probable that starvation was at least usually the cause of death. In both cases spring was the time of the attack, but in neither were toads observed in proximity to the diseased fish; indeed, in that part of Norway where the disease existed, toads are almost unknown. One cause only has as yet suggested itself to me, and that is the presence of diffused mud in the water. As both in Norway and Cirencester, works had been undertaken, just previous to the outbreak of the disease, which had had the effect of introducing a large amount of clay into the water, and the “early days of spring” were so far implicated that they were days of rain and melting snow, and thus the products of degradation were added to the mischief caused by the hand of man.
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CROTCH, W. [Letters to Editors]. Nature 2, 67 (1870). https://doi.org/10.1038/002067b0