of the Fishery Board for Scotland. 



377 



both fishes, contrary to my expectation, oospores were more numerous 

 than in those individuals which had been inoculated with oospore-bearing 

 material.' It is rather to be regretted that proof was not then made 

 manifest at this time by a further experiment, whether or not the change 

 of site was the principal factor in determining successful infection. In 

 the following year Mr Murray again prosecuted like experiments. On 

 February 1st, he applied to the head, by gently rubbing, fungus derived 

 from flies as before, on which few oospores were present, and in four days 

 the disease appeared in the region rubbed, and the fish, as usual, showed 

 signs of irritation followed by languor, and died on the fourteenth day fol- 

 lowing the inoculation. On the 12th February the experiment was again 

 repeated, but this time with fungus bearing very few ripe zoosporangia but 

 many oospores. No result was obtained when examined eight days later, 

 but it was found to be extremely diseased wheu seen on the twenty-second 

 day after inoculation. Mr Murray infers from other observations that 

 the infection was due to the oospores which might have germinated in 

 about fourteen days after inoculation. 



In the Fisheries' Exhibition in London, the disease appeared and 

 destroyed a considerable number of fish, and as this coincided with the 

 fact that at the same period the tank water contained much lime, owing 

 to the presence of this substance in the rockwork which had been but 

 newly built, Mr Murray, at the suggestion of Professor Huxley, devised 

 and prosecuted a series of experiments in order to determine whether or 

 not the presence of lime in the water conduced in any way to the onset 

 of the disease. His experiments consisted in inoculating a double series 

 of fish, one of which was kept in ordinary water while the other was 

 supplied with water containing one-half per cent, of lime. In one set of 

 experiments, he succeeded in getting the fish inoculated, both those in the 

 ordinary as also those in the lime water, when it was found that death 

 overtook the latter at an earlier period of the disease than it did those in 

 the former case. 



From the wide-spread occurrence of this fearful disease, sometimes in 

 a sporadic, at other times in an epidemic form, the popular mind has 

 been much exercised, particularly of late years, as to the cause of this 

 curious condition, and as a result of this all sorts of views have been 

 promulgated regarding its causation. 



The pollution of rivers as a cause found favour with many persons, but 

 is easily met and refuted by the fact that in many cases the disease 

 occurs in rivers and ponds entirely free from the slightest suspicion of 

 pollution. There can be no doubt whatever that the prime cause lies in 

 fungus, and that without its presence no disease can appear, but when we 

 consider that the presence of fungus on a few fish in a river will result in 

 a few days' time in affording a plentiful harvest of spore germs, sufficient 

 to infect every Jish in the river, the question then arises, why it is that so 

 very many fish escape. Do healthy fish possess an immunity 1 This 

 seems scarcely likely in view of Professor Huxley's report, but, on the 

 other hand, they do not seem so easily infected as one might suppose, and 

 therefore, there arose another theory that a previous injury was requisite 

 in order that the fish should take the disease. That a mechanical injury 

 is unnecessary is pretty well proved by observations of fish taking the 

 disease, while in situations remote from any chance of injury, as in 

 aquaria, etc., and still further by Mr Murray's success in infecting fish 

 while in a healthy state. We must, however, note that it is possible for 

 a fish to be in an abnormal condition of health, without giving visible 

 evidence of it, and further, of the diseases peculiar to fish we have only 

 the most meagre conception. We find that at the Howietoun fisheries, 



2 b 



