BLINDNESS IN MARINE F1SIIE3. 637 



jihsoiption of food. Not uii frequently, moreover, such examples 

 }>ret-eut a cei'taiu broken-backed appearance, ■which, so it is stated 

 by the attendant in charge of the tanks, is due to the fish, when 

 fii'st installed, persistently hammei'ing themselves against the 

 glass ! 



3. Cornecd Ojjacitis and Cataract in Pollack 

 (Gadus pollachius). 



The Pollack forming the subject of the present note wei'e four 

 young specimens ranging from 74 to 85 inches in length. At 

 the time when they came under the writer's obsei'vation (in Sept. 

 1912) they had lived in the Aquarium, in a tank apart from 

 otlier fish, for a period of about nine months. When first 

 installed their sight apjjeared to be normal ; but it seems that 

 these particular fish had been taken on a position close inshore 

 off" Shoreham, where there is an outflow of chemical waste. 



Mr. E. W. Cowley informed the writer that fish which were 

 known to have come from this locality were as a laile refused for 

 stock purposes, in view of the fact that, after a shoi't period in 

 the Aquarium, they invariably showed signs of disease. Hofer* 

 states : " Trout, etc., have been frequently attacked by perforation 

 of the cornea and cataract through existing in waters impreg- 

 nated with ii'on from drains " ; and goes on to sfiy, '' It is not yet 

 established whether these consequences ai'e to be ascribed to 

 ii-on salts in general or to any particidar one." A lack of 

 similar observation, viz. : the effect of industrial wastes, 

 sewerage, etc., upon tliose marine fishes often frequenting 

 estuaries and tracts of water in which such impurities are known 

 to occur, prohibits any comparison. Yet it is a noticeable fact 

 that the examples a.bout to be described exhibit a form of 

 l)lindness most frequently met with in various freshwater fishes 

 ((?. g. Pike, Perch, Car23, etc.). 



At the time when the present specimens came under the 

 Avriter's obsei'vation, they wei'e without doubt totally blind, both 

 eyeballs of each example presenting the opaque white appearance 

 similar to that seen in the case of fish which have been boiled. 

 The cornea in every case was but slightly affected, no apparent 

 lesion being discernible on any part of the integument covering- 

 it. The geiieral transparency, moreover, was considerably greater 

 than it was in the case of either of the two pi'cceding examples. 

 On dissection it was found that the cornea protruded in front of 

 the lens to a considerable extent (cir. 2| mm.). A transverse 

 section, taken through the centi'es of both eyeballs from two of 

 the specimens, showed that the extent of necrosis attacking the 

 interlocking fibres was practically tlie same, viz., equivalent to 

 tw'o-thii'ds of the entii-e diameter of the section. Vei-tical 

 sections, ;'. e. from anterior to posterior aspect of the lens, showed 



* Op. cit. p. 291. 



