68 The Fungus of Salmon Disease. 



owing to neglect in changing the water as advised. Such a 

 state of things is, however, never met with unless when using 

 large pieces of nutrient substances, and any thing of the kind is 

 in the highest degree unfavourable to saprolegnia cultivation. 



The appearance of a fly or grub with the fungus developing 

 on it is very beautiful ; the fine growth of thread-like stems 

 standing out into the liquid in every direction seem to envelop 

 the object it is feeding on in a kind of halo, but when closely 

 observed the appearance of a tuft at the extremity of each stem 

 or hypha can be seen with the naked eye in a good light, though 

 the numberless growth of stems as they radiate from the object 

 confuses the sight, and renders them impossible to distinguish, 

 except at their ends. 



This method of cultivation is the usual one followed in watch- 

 ing the life history of our fungus : — it is only necessary to re- 

 move the fly from the tumbler on to a glass slip, and, adding a 

 little water, to examine it with a low power ; the magnification 

 of ioo diameters being in ordinary cases sufficient, though 

 higher powers can be used without the necessity of using a 

 cover glass over the objects. 



For experimental work on the life of the fungus under vary- 

 ing conditions of nutriment, temperature, or any special in- 

 fluence to be studied, cultures in tumblers are not so favourable 

 as the hanging drop cultivations, and to carry on these the 

 manipulation must be somewhat more careful. 



Flies have long been favourite objects to cultivate upon, and 

 by their use alone it would be easy to keep the fungus growing 

 favourably for years, with no deterioration or change. In this 

 way I have myself lately kept cultivations under observation 

 for five months, and they are just the same to-day as when I 

 started them from a diseased trout that was sent me by post 

 from Dumfries. It is far more difficult to cultivate in open 

 tumblers from pieces of fish or meat. Professor De Bary, of 

 Strasburg, observed long since that such objects were more suit- 

 able for bacteria and other enemies of the Saprolegnieae, and in 

 order to succeed in cultivating our salmon fungus on them, it 



