lupin and his transformations...

[silly_mr_wiggles <mmm_poptarts@misery.net>]

No: HPFGUIDX 48770

Ok, this is my first post here so be kind please!

In PoA Lupin gets the potion from Snape to keep from transforming.  
Lupin is in human form when he recives the potion from Snape.  As we 
know from the Shreaking Shack scene, Lupin didn't transform until he 
was outside in the moonlight.  This being confirmed by JKR herself. 
Now my question is this, why, if Lupin didnt transform until night 
fall in the moonlight, did Snape have to teach his classes for him on 
days of the full moon? In chapter 9 of PoA Snape stands in for Lupin 
as DADA teacher, this is explained by Lupin in chapter 17, after 
Hermione tells Harry and Ron that Lupin is a werewolf - "Lupin 
stopped dead. Then, with an obvious effort, he turned to Hermoine and 
said, 'How long have you known?' 'Ages,' Hermione wispered. 'Since I 
did Professor Snape's essay...' 'He'll be delighted,' said Lupin 
coolly. 'He assigned that essay hoping someone would realize what my 
symptoms meant....Did you check the lunar chart and relize that i was 
always ill at the full moon? Or did you relize that the boggart 
changed into the moon when it saw me?' 'Both,' Hermione said 
quietly." (PoA p346 USA Hardcover) Why was lupin healty and able to 
be there in the shack, on a night of the full moon without having 
taking his potion, but yet unable to be in his classes teaching 
earlier in the year?

-cracker (who thinks she did pretty good for her first post!)

p.s. - I am really sorry if this has been brought up before, i didn't 
see any previous posts about it when i searched. Also, in case you 
are wondering my name is Jessica and I am 14 years old.