Dr. Arrowsmith, I trust we shall do more than merely say you are welcome here; I trust we shall show you how welcome you are! Dr. Gottlieb tells me that you have a natural aptitude for cloistered investigation but that you have been looking over the fields of medical practice and public health before you settled down to the laboratory.
There are no more uses of "aptitude" in the book.
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Hyde’s study indicates that girls and boys have the same aptitude for math.
Evidently she had great natural aptitude for her work.