“natural decay and corruption of the human body” sets the mood to the reader that Frankenstein is studying the darker side of the body’s natural occurrences. Frankenstein wants to research about the corruption of humans, exposing the hidden truths that people choose to ignore. Also, death is a sensitive topic, something people would avoid thinking about. Frankenstein wants to eliminate this peace and find out what actually happens in death, to the body. These things would scare most people, causing the reader to have an unsettled feeling going further into the book.
“darkness had no effect on my fancy” tells the attitude of the protagonist, explaining that he’s not phased by the frightening aspects of his study. He finds the ideas intriguing rather than scary. Frankenstein looks at the “dark” processes of the human body more as the way of life, he sees the positive sides.