This cover reminds me of a hair-brained theory that I've been developing for some time now. Basically, it suggests that every generation (a term I use very loosely here) has a new substance of which it is terrified by. This substance can have a wide variety of effects on an individual — it can kill them outright, change them physically, corrupt them mentally, give them fancy powers or any combination of the above.
For example, in the pulps, and in early comic books, this substance was "chemicals" (See Hourman or Dr. Jekyll). By the Marvel Age of comics this substance was radiation (See Spider-man or the Fantastic Four). For a short while in the 1990s it was "virtual reality" (See "Lawnmower Man"). Nowadays its genetic manipulation. And if you look back past this modern era, you could suggest magic, fairy dust or the gods were the "substance" of the time.
Each one of these "substances" is a key element to the fantastical stories of the day, they created superheroes and they created monsters. These substances are the source of adventure and peril.
But as the real essence of these substances was revealed, they fell by the wayside to make room for the the next mysterious substance. The question is, what will be tomorrow's substance?

For a look at the history of Flynn's Detective Fiction, which changed its name to Detective Fiction Weekly, visit this Web site. That site seems to claim that DFW is still being published today, but I can't find anything to corroborate that assumption.