Dr. Filostrato believed (incorrectly, as it turns out) that he had preserved the head of François Alcasan. Towards the end of the book, it's revealed that the Macrobes didn't really need Filostrato's setup in order to be able to use Alcasan's head.
That being said, why did the N.I.C.E. bother with Filostrato in the first place? Did they believe that they needed Filostrato's setup too?