152 TENTH ANNUAL REPORT OF THE 



the last trout succumbed, two having escaped from the aquarium during 

 the course of the experiment. Of the control trout, three escaped during the 

 first week and the remaining six were alive on the twenty-second day and 

 quite without unusual symptoms or lesions. 



In addition to the above experiment, an inoculation was made directly. 

 Scrapings from the ulcers of the dead domesticated trout were implanted 

 beneath the skin and within the muscle tissue of a wild trout about 

 seven inches long. At the same time a control, five inches in length, was 

 wounded in the same way, but somewhat more severely, and water 

 injected into the wound. The inoculated trout died on the third day, the 

 wound showing evidence of progression, and the membrane about the 

 mandible showing a small inflamed area. The control remained alive and 

 recovered from its wound. Wild trout were not available to make these 

 inoculations on a considerable number, and the result, while suggestive, 

 lacks conclusiveness. 



Taken together, however, the results of feeding the ulcers and the 

 direct implantation of material taken from them make it practically cer- 

 tain that the disease attacking the trout is some form of infection. The 

 attempts to obtain bacterial cultures failing to furnish an organism, and 

 microscopical examination corroborating, the probability of a protozoan 

 infection is strongly suggested. The minute animal organisms which cause 

 disease have not until very recently been grown in artificial media, and 

 even at present, though cultures of the trypanosomes have been obtained, 

 no methods of general applicability are available. The pure culture is the 

 chief means by which the present extensive knowledge of bacteria has been 

 obtained and its lack with protozoa curtails immensely the sources of 

 information concerning them, and makes it practically impossible to 

 demonstrate by inoculation the causal relation of specific protozoa 

 to a given disease. Moreover, the resemblance of certain of the nor- 

 mal morphological elements of the tissues of the host to protozoan 

 forms, adds to the obscurity of protozoan infection, and to the difficulty 

 of diagnosis. 



Nevertheless, fish disease due to microscopic animal organisms having 

 a general distribution throughout the body, and, therefore, of the septi- 

 caemic type are recognized and several have been described from European 



