Final answer:
The advice that Debray gave to Madame Danglars is not contained within the provided text excerpts, and without the correct context from 'The Count of Monte Cristo', it's impossible to provide an accurate answer to the question.
Step-by-step explanation:
The advice that Debray gave to Madame Danglars is not directly referenced in the text excerpts provided. Therefore, based on the given information, it is not possible to ascertain what advice Debray specifically gives to Madame Danglars, as the character Debray does not appear in these excerpts.
The text elements you provided are from various literary works, including a mention of Dupin, a character by Edgar Allan Poe. However, none of these excerpts feature Debray or Madame Danglars, which are characters from 'The Count of Monte Cristo' by Alexandre Dumas. Thus, without the appropriate context or text, I am unable to provide the advice given by Debray to Madame Danglars.
Debray suggested this as a way to help the Prefect find the missing letter and solve the case. By conducting a thorough search of the premises, they would have a better chance of finding any clues or evidence that could lead them to the letter.
This advice shows Debray's practical and logical approach to problem-solving.