"Tissue samples, yes, for experiments." Sherlock says it as though it ought to be obvious -- which in his mind, it really ought.

"Don't know how I'm to be expected to entertain myself without them. Be bored otherwise." Which, judging by his tone, is the absolute worst of all possible outcomes. It is, in truth. Sherlock bored is one step closer to Sherlock lost entirely, or at least one step closer to him doing something really awful.

"Be an awful flatmate when bored; you wouldn't want that. So." So it's nearly generosity, isn't it?