The most helpful strategy that can be used to determine the meaning of the word "scalpel" is the use of context.
If one does not know the meaning of the word "scalpel" used in this excerpt from "The Hot Zone" a good way to infer its meaning would be through the analysis of the context.
With the information given, we can deduce that the scalpel is a sharp object used to cut things, in this case: flesh. A woman cutting flesh with "gloved fingers" (meaning she is wearing gloves) produces the image of a doctor.
With this in mind, one can deduce that a scalpel is a medical tool used to cut open pacients.