(1) Observations were made of the symptoms that appear in the eye fundus of the goldfish when the fish are exposed to an unfavorable environmental medium. Such a medium was prepared usually by disolving a drug in the normal rearing water.
(2) Such methods of ophthalmoscopy by which the eye fundus of the goldfish can be examined without injuring the fish were invented. Consequently, it was possible to examine the eye fundus of the same individual of fish repeatedly.
(3) A total of 54 kinds of drugs were used singly for rendering the rearing media unsuitable for the life of goldfish. As a rule, typical symptoms of both incipient stage and dying condition caused by each of the drugs were recorded in natural color photographs.
(4) In each experiment, some of the fish which presented symptoms of incipient stage in the eye fundus were put back in the normal rearing medium, and their vitality was observed during the following one month.
(5) The effects of metabolic wastes accumulating in the environmental medium, of laboring breath and of hypertonic environmental medium upon the eye fundus of the gold fish were also observed.
(6) Lastly, the symptoms shown in the eye fundus of the goldfish killed instantly by clubbing were compared with of the fish agonized to death by being left in the air.
(7) The eye fundus of the goldfish were sensitive to 34 kinds of the examined drugs. Harmful effects of these drugs on the vitality of the fish could be successfully avoided by removing the fish into a normal rearing medium upon finding the eye fundus synptoms of incipient stage. The rest of the examined drugs mostly caused characteristic symptoms in the eye fundus of the goldfish.
(8) The eye fundus of the goldfish was highly sensitive to the accumulation of metabolic wastes in the environmental medium, but not so sensitive to the effect of laboring breath or to the hypertonicity of the environmental medium.
(9) The goldfish killed instantly could be distinguished from those agonized to death by examinating their eye fund.