In the White Vincent Method, the diluting vehicle must be isotonic.

• A. The diluting vehicle must be isotonic
• B. The diluting vehicle can be isotonic or hypertonic
• C. The diluting vehicle must be hypertonic
• D. The diluting vehicle must be hypotonic

Answer: (A)

Osmotic balance matters: solutions that are isotonic have the same osmotic pressure as body fluids, so they don’t cause water to rush into or out of cells. In the White-Vincent method, using a diluting vehicle that is isotonic is essential because it keeps the red blood cells’ (or other cell-based) volume stable during the test. If the diluent were hypertonic, cells would shrivel as water leaves them; if hypotonic, they would swell and potentially burst. Either scenario would create artifacts and obscure the true tonicity of the test substance. By using an isotonic diluent, any observed effects reflect the properties of the test material itself, not the diluent’s osmotic action.