XI 



whether that is so or not, we assume, with the scientific witnesses 

 who have come before us, that the seeds of Saproleg?iia are 

 generally present, and that the disease therefore is not a new one. 



If this be so, it seems to follow that, for some reason yet to be 

 explained, the Saprolegnia which has existed in a sporadic form 

 has — to use a technically inaccurate but expressive word — become 

 " epidemic " of late years. On a small scale, this seems certainly 

 to have occurred at Ightham in Kent. An epidemic of Saprolegnia, 

 the cause of which is unexplained, broke out among the coarse 

 fish in the moat surrounding an old house in 1850 and 1874. 

 We reprint in the Appendix the full account of this epidemic* 

 It is sufficient for us to add that what occurred at Ightham 

 may occur and has occurred at other places, and that just as 

 sporadic cases of typhus, cholera, or ringworm may be stimulated 

 into epidemics by various exciting causes, so sporadic cases of 

 Saprolegnia may become stimulated into a salmon disease. 



What then are the circumstances which have made the Saprolegnia 

 epidemic? We print as an addendum to this report an analysis, 

 drawn up by one of us, Mr. Buckland,f which expresses his-opinion 

 of the causes of the disease which have been brought forward by 

 various persons. It is sufficient here to say that no one hypothesis 

 which has yet been suggested stands the test of careful criticism. 



All the different circumstances and conditions which were stated 

 by different witnesses to be the causes of the disease are to be found 

 existing in rivers where the disease has never been heard of. 

 We have found the disease existing in polluted and in pure 

 rivers ; in rivers obstructed by weirs and in rivers where there are 

 no obstructions ; in understocked and in fully- stocked rivers ; in 

 rivers flowing from or through lakes and in rivers with no lakes 

 belonging to their catchment basins ; in short, in rivers with 

 the most opposite physical features : and we have been unable to 

 detect in the Tweed, Nith, Annan, Doon, Esk, Eden, and other 

 rivers attacked by the disease any special conditions to which the 

 disease can be attributed, which are not likewise to be found in 

 some of the rivers which have escaped its ravages. Those who 

 are acquainted with only one or two salmon rivers are rather apt 

 to imagine that in the pollution, obstruction, or overstocking of 

 the rivers with which they are familiar they have discovered the 

 true cause of the disease. But to those who have an extensive 

 acquaintance with the salmon rivers of Great Britain, the most 

 perplexing thing connected with the present inquiry is that every 

 cause, without exception, which has been assigned as the true 

 origin of the salmon disease in infected rivers, is to be found in 

 rivers where no disease exists, or has ever been known to exist. 



We have thus been unable to ascertain for certain any one cause 

 which would satisfactorily account for the epidemic character of 

 the recent outbreak of Saprolegnia. Such a cause, however, must 

 undoubtedly have arisen from one of two circumstances. Either 

 (1) the fungus itself must have recently been stimulated into 



* Appendix III., p. 117. 

 | See p. xiv. 



