56 THE TKUB SALMON DISEASE 



germinate upon any dead animal substance. Thus it has 

 now been shown that the fungus which hitherto has been 

 regarded as the disease itself is not pathogenic; it only 

 takes advantage of the morbid condition brought about 

 by the more subtle bacillus. 



Then, it may be asked, how is this to be reconciled 

 with Mr. Murray's success in producing salmon disease in 

 healthy fish by inoculating them with the fungus ? It is 

 explained by the invariable presence of numerous and 

 rapidly multiplying colonies of the real pathogenic 

 bacillus in Saprolegnia growing upon diseased salmon. 

 It is an operation of the greatest delicacy to obtain a 

 culture of the one without including any of the other; 

 and this operation, of course, could not be even attempted 

 until the true micro-organism of the plague had been 

 identified. Mr. Murray believed that he had transplanted 

 the disease from salmon to dead flies, and from dead flies 

 to live fish, by a process of inoculation with the pure 

 culture of Saprolegnia. What he really did was to 

 inoculate with a culture of Saprolegnia, plus a culture 

 of Bacillus Salmonis Pestis. 



But Mr. Patterson obtained absolutely pure and distinct 

 cultures of both these organisms. Healthy fish inoculated 

 with Saprolegnia only suffered no whit, for that growth 

 can only be established on dead tissue ; but healthy fish 

 inoculated with the new bacillus speedily perished with 

 the usual symptoms of disease, including the growth of 

 Saprolegnia in the diseased areas. - 



Having thus arrived at a precise knowledge of the 

 cause and nature of the salmon disease, we are so far on 

 the right road to contrive means to check or prevent 

 it. Much of the supposed advance hitherto made has 



