... centrifugation. The erythrocytes form the lowest layer, while the leukocytes and platelets form the next layer, also known as the buffycoat. The Pluripotent Stem Cell The hematopoietic stem cell is the ... used either alone, or in conjunc-tion with the original First Aid for the USMLE Step 1. In this way, students can tailor their own studying experience, calling on either book, according to their ... com-panion, First Aid for the Basic Sciences: Organ Systems, are designed to fi ll the need for a high-quality, in-depth, conceptually driven study guide for Step 1 of the USMLE. They are designed...