Due to a very severe outbreak at the end of the 1760s, some of the best-known names in Dutch medicine became involved in the struggle against the disease. Several independent trials were begun, most notably by Pieter Camper in Groningen and Friesland. The results of his experiment in Friesland were encouraging, but they proved to be the exception; testing by others in the provinces of Utrecht and Friesland obtained disastrous results. As a result, the Frisian authorities concluded in 1769 that the cause of rinderpest was God's displeasure with the sinful behavior of the Frisian people, and proclaimed 15 November a day of fasting and prayer. Interest in inoculation declined sharply across the country.