We didn't have a midterm per se but this semester all of our exams (including the impending final) are 70% new + 30% old material. They are also only 50 questions... 25 for lecture material and 25 for lab material.
Ours are all cumulative, and a subjects worth on the exam is generally proportional to how much of it we did in class. Though there are some exceptions (eg, reproductive physiology was its own seperate exam)