The chemical is a protein that prevents the Wraith from feeding. When the Wraith attack a human they inject something through their fingers, which allows them to then withdraw life/energy/whatever from the human being. This protein interacts with the Wraith chemical preventing this from happening.
They use a terminally ill Hoff as a guinea pig, using the Wraith they have captured, which allows for a discussion of the moral arguments and a Doctor's oath to 'first do no harm'.
They then find that the protein not only defends against, but also kills the Wraith attacker. So we lose the captured Wraith without him giving any useful information.
They then worry that, rather than leave the Hoffs alone, this threat will now mean that the Wraiths will actually seek them out and destroy them all.
They then discover that the Hoffs have gone to a full innoculation program without more safety tests, and that the protein also kills 50% of the Hoffs too. The Hoffs, however, still vote 98% in favour of this program being completed. The team leave, telling them that can no longer help them, and that when they return they will most likely find them all dead.
As you can see, this was a 'fun', happy little ep. It was also very slow. You CAN make scientific research look more interesting than holding up coloured testubes, and reading books to some background music.
There was another reference to the original Star Trek series, which must be compulsory viewing for Stargate personnel.
The lack of budget seriously affects these kinds of stories, because the Hoffs were just not alien enough. They have a technology level of around our 1900's. But that does not mean that they would wear clothes and have hairstyles that were popular on Earth at that time. Why would the men wear ties but not the women? Why would lighting, fans, cupboards, doors and tables be of a similar design?
In the original series of Star Trek they quoted 'Hodgkins' law of parallel planet development to explain why so many humanoid beings and cultures resemble Earth throughout the Galaxy. But I always like Stargate because the Goa'uld were a believable reason for this in our Galaxy. It was the perfect explanation, but no longer works in the Pegasus Galaxy.
It seems that they just don't care about this any more and it is a shame.
On the other hand, everyone has spoken American English since the second season of Stargate SG-1 and no one explains that either, so maybe the lack of attention began much earlier.
