382 Prof. T. H. Huxley. Pathology of the [Mar. 2, 



One vast open sore may cover the top of the head from the snout to 

 the nape, and may extend over the gill covers. The edges of the fins 

 become ragged ; and, sometimes, the skin which invests them is so 

 completely frayed away that the fin-rays stand ont separately. 



Although the affection of the skin appears, usually, if not invari- 

 ably, to commence in the scaleless parts of the body, it does not stop 

 there, but gradually spreads over the whole of the back and sides of 

 the fish, though I have not yefc seen a specimen in which it covered the 

 whole ventral surface. The disease extends into the mouth, especially 

 affecting the delicate valvular membrane attached to the inner sides 

 of the upper and the lower jaws. It is said to attack the gills, but 

 there has been no sign of it on these organs in any fish which I have 

 had the opportunity of examining. 



Fish which succumb to the disease become weak and sluggish, 

 seeking the shallows near the banks of the river, where they finally 

 die. 



The flesh of a salmon affected by this disease presents no difference 

 in texture or colour from that of a healthy fish ; and those who have 

 made the experiment declare that the flavour is just as good in the 

 former case as in the latter. So far as my observations have gone the 

 viscera may be perfectly healthy in the most extensively diseased fish ; 

 and there is no abnormal appearance in the blood. 



It is known that a disease similar to that described is occasionally 

 prevalent among salmon in North. America and in Siberia ; and I do 

 not see any ground for the supposition that it is a novelty in British 

 rivers. But public attention was first directed to it in consequence of 

 its ravages in the Solway district a few years ago ; and, in 1879, a 

 Commission was appointed by Sir Richard Cross, then Home Secretary, 

 to inquire into the subject. 



The evidence taken by the Commissioners* leaves no room for doubt 

 that the malady is to be assigned to the large and constantly in- 

 creasing class of diseases which are caused by parasitic organisms. It 

 is a contagious and infectious disease of the same order as ringworm 

 in the human subjent, muscardine among silkworms, or the potato 

 disease among plants ; and, like them, is the work of a minute fungus. 

 In fact, the Saprolegnia which is the cause of the salmon disease is an 

 organism in all respects very closely allied to the Peronosjpora, which 

 is the cause of the potato disease. 



It is a very curious circumstance, however, that while the Perono- 

 sjporce are always parasites — that is to say, depend altogether upon 



* " Eeport on the Disease which has recently prevailed among the Salmon in the 

 Tweed, Eden, and other Rivers in England and Scotland." By Messrs. Euckland, 

 Walpole, and Young, 1880. 



See also the three valuable communications to the " Proceedings of the Eoyal 

 Society of Edinburgh," made by the late Mr. A. B. Stirling in 1878-79. 



