BY T. HARVEY JOHNSTON. 129 



skin between the epidermal cells, which were more or less 

 destroyed. The underlying narrow layer of dermal 

 muscular fibres did not seem- to be much affected, though 

 the connective tissue of the dermis was apparently injured 

 or destroyed, especialty between these dermal fibres and the 

 adjacent body musculature. The latter readily broke up 

 into bundles or even into fibres, this no doubt being due to 

 the destruction or loosening of the surrounding connective 

 tissue. 



Hofer* mentions that according to the duration of the 

 disease, there may be prodviced only ej)ithelial injuries or 

 a complete destruction of the subcutaneous kyers, or there 

 may be relatively deep crater-like erosions into the muscu- 

 lature even in living fish. He goes on to say that it has not 

 been definitely determined whether the destruction of the 

 €ells surrounded by the h3^phse which nourish themselves by 

 diffusion of the cells' contents, is caused by a toxin produced 

 b}- the fungus, or whether it is the result of a loosening of 

 the cells from their surrounding structures and a 

 deprivation of their oxygen supply. 



In sections of the branchiae one could readily see that a 

 large amount of gill substance had been destroyed by the 

 fungus. The spaces between adjacent gills and between 

 the two hemibranehs of the same gill were choked up Avith 

 blood and mucus, the blood cells in places forming relative!}^ 

 large masses or clots continuous with the eroded ends of 

 ruptured branchial blood-vessels. The epithelium of the 

 gills was'destroyed, as also were the branches of the branchial 

 veins on the outer side of each hemibranch, though the 

 capillaries extending between the arteries and veins w'ere 

 intact, probably being protected by their deejjer situation 

 in the gill substance. Sometimes the branches of the 

 branchial arteries were eroded. Commonly it was impossible 

 to determine the outer limits of the gill owing to the destruc- 

 tion of the epithelium and the superficially situated blood 

 vessels, w^hether afferent or efferent branchials, whose 

 contents merged into the surrounding clots. The latter 

 were penetrated by hyphse as also was the gill tissue itself. 

 The mere presence of the fungus would act mechanically 

 as a hindrance to the free circulation of water through the 



* Hofer. /. c, p. 101, pi. 10. 



