10 



But there is a large number of these moulds which are 

 not saprophytes, but parasites ; that is to say, they attack 

 living animals and plants, and in many cases destroy them 

 with great rapidity. The silk-worm culture is sometimes 

 ruined by the so-called " muscardine " disease, caused by 

 a mould, the Botrytis bassiana, which enters the body of 

 the silk-worm and destroys its substance. 



In some autumns, our common domestic flies are des- 

 troyed in prodigious numbers by another curious mould, 

 the Empusa muscce. Even mankind are not free from the 

 attacks of fungi, as in the ringworm of children's skins. And 

 as to plants, multitudes of destructive epidemics of which 

 the smut of wheat and the potato disease are the most 

 notorious, are produced by parasitic fungi of various 

 kinds. 



As a general rule, fungi are either saprophytes or para- 

 sites that is to say, they live habitually either on dead or 

 living organic bodies. 



Now the Saprolegniaferaxw\\\d\, as we have seen, forms 

 the cottony covering of the diseased salmon skin, is habi- 

 tually a saprophyte, especially found on dead insects ; and 

 when it was first discovered to be a constant concomitant of 

 the salmon disease, there was very good reason for suspecting 

 that it might be a saprophyte, preying on the dead tissues 

 of the skin destroyed by a precedent affection, and not a 

 parasite, the presence of which was the true cause of the 

 destruction of the tissues. 



When I addressed myself to the study of the disease 

 two years ago, therefore, I endeavoured in the first place to 

 obtain conclusive evidence on these two points. I. Is the 

 saprolegnia of the salmon the cause or only the concomitant 

 of the disease ? Is it the real enemy or only a camp-follower ? 

 2. If the Saprolegnia of the salmon disease is a true para- 



