What is the nature of Renfield's madness? In what sense does Renfield's madness parallel Count Dracula's behavior

Dr. Seward reports on the strange behavior of Renfield. Renfield is fascinated by animals that devour each other. He catches flies and feeds them to spiders, and he also eats the insects himself. He catches some sparrows and begins feeding the spiders to them, and he eventually asks Dr. Seward if he can have a kitten. Dr. Seward refuses. The next day, the sparrows are gone. Dr. Seward asks where they went, and Renfield responds cryptically that they all "flew away," but there are feathers around the room and blood on Renfield's pillow. Later, he vomits up feathers. Seward invents a new classification for Renfield, calling him a "zoophagous" (life-eating) maniac. Renfield seeks to "absorb as many lives as he can." Dr. Seward's journal reveals a wish to experiment further on Renfield, although the idea seems to trouble him ethically. And he expresses a wistful envy for Renfield, because the madman has a purpose.

A parallel in behaviors would be the consumption and desire for the life source of blood.