SEA-FISHERIES LABORATORY. 299 



abundant at this time, but about the middle of October 

 the epidemic bad greatly subsided, though even then 

 about 10 per cent, of the salmon parr observed 

 seem to be infected. The extent of skin affected in the 

 case of specimens caught at this time also appeared to be 

 less than formerly was the case. All this time salmon 

 parr alone were infected. Brook trout do not appear to 

 have suffered. 



Fig. 5 (pi. VIII) represents the tail portion of one of 

 these fish with a characteristic skin lesion. In all cases 

 the naked eye appearance was pretty much the same as 

 that figured, though not always so prominent. In the 

 less strongly infected fishes the skin. appears to be covered 

 in places with a thin, whitish scum, like felted or com- 

 pressed cotton wool. This can easily be rubbed away 

 and then the skin underneath appears to be quite normal, 

 the scales retaining their usual appearance. Here and 

 there this growth is, however, much more prominent. 

 For instance, in the case figured there was a raised 

 whitish tumour on each side of the body just above the 

 anal fin. This growth was raised about 2 mm. above 

 the surface of the skin. It had usually a slightly 

 crenulated margin and had surface markings indicating 

 roughly the position of the scales underneath. In the 

 case of some of these larger growths, however, the skin 

 underneath the adventitious tissue was disorganised and 

 the scales came away easily. 



Microscopic examination showed no traces of a 

 mycelium so the presence of a fungus was out of the 

 question. Neither were there any traces of Myxosporidia. 

 These were specially looked for as the naked eye 

 appearance of some of the fish was not unlike the con- 

 dition of " Beulenkrankheit " (Myxoboliasis). Smears 

 were made from the blood and from all the visceral organs, 



