All graduate and professional courses offered in the University are described on each subject page. The unit of credit is the semester hour, which involves one hour of theory or from two to four hours of practice per week for one semester of 15 weeks. Figures following the credit hours indicate the contact hours per week devoted to theory and practice, respectively. Theory includes recitations and lectures; practice includes work done in a clinical setting, laboratory, shop, drawing room, field or other.  When courses are cross-listed, credit cannot be received for both courses. Any course may be withdrawn from the session offerings in case the number of registrations is too small to justify offering the course.