Chemotherapy drugs are often given over a series of daily visits followed by a few days or weeks rest. Each dosage series is called a course. Chemo treatments are carefully monitored by a team of specialists through blood tests and physical examinations. One of the major early side effects of chemotherapy is the lowering of white blood cell counts, the chief cells that fight infection. The suppression of white blood cell counts leads to a lowering of the immune system, leaving patients vulnerable to infection and disease. The count is checked before giving medications. If it drops so low that there is danger of serious infection, there may be a pause in therapy while the body recuperates. Because many of the drugs are either activated or eliminated from the body by the kidneys or the liver, doctors also watch the functions of these organs carefully.