The Relationship between Inquiry into the Cause of Minamata Disease
and Social Action preventing the Epidemic

Kumamoto University, Department of Law

1. The epidemic of Minamata Disease

Minamata is an industrial city of Japan. The Chisso Corporation's Minamata Factory produced various chemicals. Industrial effluents flowed into Minamata Bay. A mysterious nervous illness had affected fishermen and their families living near this bay. In 1956, this nervous illness was recognized as an epidemic and called " Minamata Disease ".
From 1952ュ53 abnormal phenomena caused by pollution had been often observed in the bay; a great amount of abnormal death of shellfishes and floating of many large sick fishes. Furthermore, many cats showed strange behavior and died in the area where the epidemic of Minamata Disease broke out. These behavior of sick cats was called cats' "dancing disease" by inhabitants and suspected to be caused by damages of the nervous system.

2. Two bioassays using cats

(1) In 1957, Dr. Hasuo Ito, head of the Minamata Public Health Center, proved first the toxicity of fishes and shellfishes in Minamata Bay using cats. He gathered fishes and shellfishes from Minamata Bay and gave them as food to normal five cats from March to July in 1957. All of them showed the symptoms of "dancing disease" 7 or 48 days later. These results clearly suggested that fishes and shellfishes in Minamata Bay were contaminated with toxins causing "dancing disease" in cats.

(2) In 1959, Dr. Hajime Hosokawa, director of Chisso Minamata Factory Hospital, tried to clarify whether the effluent discharged from the acetaldehyde plant caused Minamata Disease. He gave 20 ml of this effluent to a normal cat at each meals. About 80 days later, he found that the cat showed the typical symptoms of "dancing disease". This result was ignored by the executive of Chisso Minamata Factory. Dr. Hosokawa could not publish a report nor continue this bioassay using cats.

3. Summary

Dr. Ito's bioassay suggested the necessity of an urgent ban on fishing in Minamata Bay, so as to prevent the epidemic of Minamata Disease. However, the ban was not enforced by the government. According to the result of Dr. Hosokawa's bioassay, it was necessary that the director of Chisso Minamata Factory immediately stopped the discharge from the acetaldehyde plant. However, he continued the discharge without any investigation. The two bioassays contained very important information enough to prevent the expansion of Minamata Disease, even if the chemical structure of causal material of Minamata Disease was not determined. However, both the government and Chisso Corporation ignored those results, and the epidemic of Minamata Disease showed the extremely wide expansion.