Based on Rane's answer:i m guessing it would be a permanent effect;you take it he loses it,untill he replenishes it.So i think it would indeed be 10hp x 10 sec = 100 hp.
But then it could also be that he loses 10 hp (char of 100 hp going to 90 max. for a period of time and you getting +10 max)after that he can replenish health up to 100 and you up to your normal.
Arg

i hate this... can't say i have learned the spells...I mean,am i just thinking like an idiot is it just not that simple?
Still i 'd go with choice nr 1...much cooler
