When you're in the thick of chemo, your numbers–your blood cell counts–become a vitally important thing to know. Here’s a quick refresher: Red blood cells carry oxygen and bring energy to your organs and tissues, while white blood cells, sometimes called your "natural defenses," shield your body from bacteria and viruses that cause infection. When counts are low, especially white cell counts, you're at great risk of developing illness and fatigue. We've had a lot of search traffic for this article lately, so we thought we'd spotlight it again. Learn to protect yourself and your fighter cells -- so you can recover successfully from chemotherapy's drain.