Complex sentence: McCollum captured some rats from a horse barn but they were too vicious and wild, so he replaced them with twelve young albino rats with some domestication that he bought for $6 from a Chicago pet store.
Split into simpler sentences: McCollum captured some rats from a horse barn but they were too vicious and wild. He replaced them with twelve young albino rats with some domestication that he bought for $6 from a Chicago pet store.