KUNMING, Dec.28 - Altogether 248 students fell sick after eating a school lunch including kidney beans in Southwest China's Yunnan Province on Thursday, local authorities confirmed early on Friday.Investigators suspected the beans were undercooked.The students, from Zhuyuanzhen Township High School in Fuyuan County, complained of vomiting and nausea late Thursday afternoon and were put under medical observation at night, a spokesman with the Fuyuan County government said.By 8:00 am on Friday, about 170 students were still under observation at four local hospitals.Hospital sources said none of the cases was critical.Kidney beans contain lectin, a toxic agent that can cause diarrhea if the beans aren't heated thoroughly, according to health officials.