Why did Morgulis Resigned?

We have been playing out the game 1 in the book The Sorcerer's Apprentice by David Bronstein and Tom Furstenberg, published by Cadogan Chess. After Bronstein's 34th move, his opponent Morgulis L. resigned. Now we have tried to play through the game and found that black has more than a couple of ways to stop white's attack. As our "move of last resort" we entered the board position into HIARCS 9 and even the chip cant find the best continuation.

Why did he resign?

Here is the position after 34. Bxf7:

(1) Bronstein, D - Morgulis, L.

Pioneers Palace Championship,

Kiev, 1940

[C26] Vienna Opening