Final answer:
The statement is false; capillary tubes used to collect blood for medical analysis through capillary action do not need to be filled with a special clay before centrifugation.
Step-by-step explanation:
The statement that a capillary tube must be filled with a special clay before centrifugation is false. Capillary tubes are used in medical analysis to collect blood by capillary action, which is a process where a liquid rises or falls inside a narrow tube due to the relative strength of cohesive and adhesive forces. When blood is centrifuged, the objective is usually to separate plasma from cellular components. If additional material, such as a special clay, were to be added, it could potentially contaminate the sample or interfere with the separation process. Therefore, capillary tubes do not require filling with a special clay before centrifugation.