ICHTHYOLOGY. 23 



less, the fins pallid, and the eye abnormally yellow, while 

 a malignant pustule often shows itself beneath the 

 scales, which gradually drop off. Epidemics, too, of 

 various types, from time to time break out among fish in 

 different waters. Some years ago a disease appeared 

 among the grayling in the river Itchen, and hundreds 

 died, rising to the top of the water, as if poisoned by coc- 

 culus indicus. Last summer a kind of " scarlet fever " 

 manifested itself among eels, at least so said the natu- 

 ralists. For some weeks after the opening of the West- 

 minster Aquarium many species of fresh- water fish were 

 afflicted with a kind of fungoid growth over their whole 

 bodies, and there was a great mortality among the deni- 

 zens of the tanks. The hardness of the water had pro- 

 bably something to do with this, and it probably also is 

 the cause of the same or a similar disease among fish in 

 private aquaria. Fish thus affected may be successfully 

 treated by a solution of bichloride of mercury, say 18 grs. 

 to 6 oz. of water. Take the fish and first rub off the fungus 

 with a brush or cloth or fingers, and then, with a camel's- 

 hair brush, paint the affected parts of the body with the 

 solution. All this can be done in a few seconds, and one 

 application will generally be found sufficient. The water, 

 however, of the aquarium should be changed daily for some 

 time. It is hardly necessary to add that fish are very sen- 

 sitive to the poisonous refuse of mines and chemical works, 

 and sad havoc has been played in more than one river of 

 late years by this abomination : and it is evident that the last 

 Act of Parliament in reference to the Pollution of Eivers 

 requires considerable amendment before it will efficiently 

 protect fishfrom what is really most wanton destruction. 

 Fish are also very susceptible to magnetic influences 



