IJY R. GREIG SMITH. 353 



Other fishes develop small white ulcers on various parts of the 

 epidermis. Beneath the skin and under the sores the muscle is 

 hsemorrhagic. The scales fall off from these places, the epidermis 

 disappears, and the muscle becomes exposed. This has a reddish 

 colour, while the epidermis at the margin for about one-sixteenth 

 of an inch is white, so that the combination of colours gives the 

 sore a striking appearance. Although these are of the nature of 

 ulcers there is no appearance of pus. It is possible that the 

 black ophthalmia and the production of these ulcers are due to two 

 different causes, but at the beginning of the investigation it was 

 believed that only one disease was affecting the trout. 



The post-mortem examination of many carcases that I received 

 showed that the body organs were apparently healthy, and that 

 they were practically sterile. Neither moulds nor algse could be 

 detected on the ulcers, in the orbital capsule or on the partially 

 affected eye. The muscles and organs when examined in the 

 fresh condition were free from parasites. But under the small 

 unbroken ulcers coccoid forms, occurring singly and in groups, 

 were detected, and from these a pure culture of a white micro- 

 coccus which had all the cultural and other characters of Micro- 

 coccus pyogenes, (Rosenbach) Migula, was obtained. 



In mammals this bacterium is responsible for the formation of 

 ulcers, boils, etc., containing pus, and the presence of pus may be 

 said to be the only difference between the ulcers of the trout and 

 those of the higher vertel^rates. As the pyogenic bacteria are 

 not known to produce pus in the epidermal lesions of fishes, it 

 seemed probable that the disease would be reproduced by inocu- 

 lating the micrococcus into healthy trout. 



To test this point Mr. J. A. Brodie, of the Department of 

 Fisheries, enabled me to infect several trout at the Prospect 

 hatcher}^ The inoculations took place some time after the 

 isolation of the bacterium, because it was not until about two 

 months had elapsed that a constant supply of water could be 

 obtained. Six healthy trout were inoculated with a suspension 

 of the micrococci in normal saline under the epidermis of the 

 posterior region, between the median and dorsal lines. After the 



