66 The Fungus of Salmon Disease. 



Few organisms are so sensitive in their demands for oxygen, 

 and its influence can be watched all through its life history ; 

 indeed, a deprivation of oxygen will arrest development at any 

 stage of growth. 



Regarding the next condition, that of nourishment, our 

 salmon disease fungus requires a solid nidus, or ground (so to 

 speak), where the spore or seed can readily germinate by send- 

 ing down branches that penetrate until they find a suitable 

 supply of food. This food is conveyed to the stems, and growth 

 goes on until the outgrowing hyphae have attained their full 

 length ; the circulation of protoplasm then becomes visible, and 

 is soon followed by spore formation and liberation. The growth 

 of the fungus is indeed very like that of grain ; it has roots and 

 stems, and forms its seeds in a manner that, even in appearance, 

 justifies the comparison. It is probable that it draws its nour- 

 ishment mainly from the ground or nidus in which it is rooted ; 

 and if the stems be torn from their roots, or the roots be taken 

 from the soil (so to speak) on which they are growing, the plant 

 dies. 



The next condition, that of temperature, only influences the 

 rapidity of development. The range of temperature at which 

 the fungus can grow best is probably between 35 and 70 or 8o° 

 Fahr. Cold retards and heat hastens its growth. Thus, at 65 

 Fahr., a generation of zoospores can be developed in twenty-four 

 hours, whereas at 3 5 or 40 Fahr. it would take several days to 

 produce the same result. 



The cultivation of the salmon disease fungus is a very simple 

 matter indeed. There is no difficulty in keeping it growing in 

 a room for an indefinite time, when a start is once made ; and 

 as it is easily visible to the naked eye, it is not even necessary 

 to examine with the microscope daily to ensure its proper keep- 

 ing, as it can be seen at a glance. Five minutes a day spent 

 in changing the water, or transferring to different vessels, is 

 enough in most cases to keep the growth secured. 



For starting cultivation it is necessary to obtain a small piece 

 of the disease from a fish, and having put it in a glass with clean 



