ON THE SAPROLEGNIEiE. 193 



develop zoosporangia. The hyphge penetrate the derma, and 

 ramify in the bundles of connective tissue ; their ramifications 

 usually end in curiously swollen extremities. Still more towards 

 the centre of an ulcerated patch, the place of the epidermis is 

 taken by the felted mycelium of the Saprolegnia, the superficial 

 layer of the derma has disappeared, small vessels have often been 

 laid open, and blood has been effused. 



However extensive the disease may be, the flesh of the salmon 

 presents little difference in texture, or in colour, from that of a 

 healthy fish, and those who have made the experiment, declare 

 that the flavour of a diseased fish is as good as that of a healthy 

 one. No morbid appearances have been observed in the viscera. 

 The death of the fish appears to be due, partly to irritation and 

 consequent exhaustion, and partly to the drain on its resources, 

 caused by the production of a large mass of vegetable matter at 

 the expense of its tissues. 



Several causes have been alleged for this disease. The first 

 supposed cause was the pollution of the rivers ; but this may be 

 easily dismissed in faith of the evidence elicited before the Parlia- 

 mentary Commission, that the disease is by no means confined to 

 polluted rivers. Although, however, not a primary cause, it may 

 have a most important secondary influence, and may determine, in 

 fact, whether in any river, the disease shall be sporadic or epi- 

 demic. 



That pollution is the primary cause of the appearance of 

 another member of this group is shown by the following state- 

 ment : — A factory for making spirit from turnips was established 

 near Schweidnitz, in Silesia, and the refuse was poured into an 

 affluent of the river Westritz, which runs by Schweidnitz, The 

 result was such a prodigious growth of Leptomitus^ that the fungus 

 covered some 10,000 square feet at the bottom of the stream with 

 a thick white layer, compared to sheep's fleeces ; it choked up the 

 pipes, and rendered the water of the town undrinkable. Of 

 course, the universal Bacteria have been brought forward as the 

 cause of the disease, having been found in large quantities on the 

 diseased spots, upon which the fungus is supposed afterwards to 

 locate itself. The Bacteria^ however, are most probably only the 

 result of a certain disintegration of the tissues by the mycelium of 



