30 THE SALMON RIVERS OF SCOTLAND 



better facilities for ascending to their spawning grounds at an earlier 

 date ; and salmon disease had not broken out. 



I am inclined to think that we are hardly able in these days to 

 estimate the change which must have taken place in the Tweed since 

 the rapid drainage from the land came into operation. The change 

 has been gradual and therefore never striking, but it has been very 

 complete. The whole district of Tweedside is like one huge farm, 

 run on the most perfect modern principles. The average rainfall 

 is not heavy, and varies apparently from 27 to 38 \ inches. Water 

 is quickly carried off not only the high land of the upper basins, 

 but the rich undulating farm land of the main valley. Floods rise 

 suddenly and last a short time. When we consider that in the Tweed 

 and its tributaries there are no fewer than eighty-three weirs, and 

 that very many of these are unprovided with fish-passes but accom- 

 panied by polluted water, the effect of a smaller normal water-level 

 and of more sudden and extreme fluctuations, is more clearly under- 

 stood. With regard to salmon disease it may be explained that 

 while it only became epidemic as late as 1878 and 1879, it was 

 present in the river long before that time. In the Severn, salmon 

 disease was epidemic about the year 1856, and the trouble seems to 

 have been recognised, and to have become more or less well known 

 as early as 1836. 



Saprolegnia of course exists in a sporadic form in ordinary water, 

 and is found to a greater or less degree in pure waters. The tissue 

 attacked by the vegetable fungus has previously been affected by 

 the action of Bacillus salmonis pestis, and unless the bacillus has 

 been at work, the fungus does not grow upon the fish. It is, there- 

 fore, the life of the bacillus which has to be studied, and which Mr. 

 Hume Paterson, the discoverer of the bacillus, has now been study- 

 ing for some time in Tweed. The presence of disease in fish in- 

 habiting pure water is never, it seems to me, so marked as in water 

 where the fish have been subjected to the health impoverishing 

 action of pollutions. Between 1880 and 1884 the Tweed police 

 removed from the water 37,969 diseased fish. In 1907 the number 

 was 4426. Certain pollutions are no doubt much more suitable for 

 the cultivation of the bacillus than others ; this aspect of the ques- 

 tion is being worked out. That salmon disease can occur, however, 

 in water believed to be perfectly pure is believed to have been 

 shown by a most marked epidemic which broke out amongst coarse 

 fish in ponds supplied with spring water at Ightham in Kent. 1 As 



1 Official Report, by Buckland, Walpole, & Young, 1880. 



