A typical first dehydrant in the described processing sequence is:

• A. Percent alcohol used as the first dehydrant
• B. Water
• C. Xylene
• D. Isopropanol

Answer: (A)

Starting dehydration with a moderate concentration of alcohol is essential because it begins to replace water in the tissue gradually, minimizing distortion. In a typical processing sequence, water is removed stepwise by immersing the tissue in increasing alcohol concentrations, beginning with something like 70% alcohol, which starts displacing water while keeping the tissue stable. As you progress, higher concentrations (95%, then 100%) continue to remove water until the tissue is fully dehydrated and ready for clearing with xylene and then paraffin infiltration. Water cannot dehydrate; it would keep the tissue hydrated. Xylene is a clearing agent used after dehydration, not a dehydrant, and while isopropanol can be used in dehydration, the first step is best represented by a percent alcohol, which starts the gradual removal of water. This is why the first dehydrant is described as percent alcohol used as the initial step.