SOMERVILLE -- Doctors from Japan came to Somerset Medical Center on Friday to discuss a type of disease that this area is well acquainted with, and Japan is becoming rapidly so: mesothelioma. While the days of seeing "asbestos snow" over Manville are over, the hospital is still seeing the effects of the refinery on its patients, and has learned lessons about the disease the delegation from Japan wanted to hear about. Mesothelioma is a form of cancer that occurs when a person is exposed to asbestos fibers, either in the work place or at home. Most people get this cancer by being exposed to asbestos for a long period of time or short-term exposure to very high levels of asbestos, such as a worker in an asbestos factory. Dr. Kurumatani Norio, a professor at Nara Medical University in Japan, said that the group came to Somerset Medical Center because it had treated patients with asbestos-related diseases from Johns Manville, which operated in Manville until being closed down several decades ago.