今天英语卡在一个句子上了，郁闷啊

On another level ,many in the medical community acknowledge that the assisted-suicide debate has been fueled in part by the despair of patients for whom modern medicine has prolonged the physical agony of dying .这个句子中的in part by为什么要用by是什么意思，另外宾语从句中嵌套的for whom 引导的定语从句的for 是哪个动词连接的介词，这个定语从句的意思我总是翻译的别扭