At the beginning of the show, as aged Barnabas appeared at the drawing room window, I wondered to myself: "Why doesn't he just go to a cow in order to revert?" But I suppose that in these dire straits, he may have felt that only human blood would be effective. And of course, Collins blood is the best of all.
The scene when Julia offered Barnabas her blood was rather sweet: Barnabas treated her in an unusually kindly fashion. He could have said, "So, doctor, you made me into an old man so that I would turn to you!" But he didn't, and he told her she had value to him as she was. And he called her by her first name. Julia went off to her lab to cry after that - or, at the very least, to compose herself - but she did make some progress with Barnabas today.
Names are interesting. When I took Japanese, we class members addressed each other in the Japanese way: Smith-san, Jones-san, Brown-san. It was a very nice Japanese class, and around about second year, Jones-san said I should call her by her first name: "Call me Mary!" But how could I call her Mary when she was, in my mind, Jones-san? So it seems quite significant to me that Barnabas called Julia by her first name today.