What are the speakers mainly discussing?

W:Dan, you know the lab you missed? You can have my notes.
M:Thank you.
W:So how are you feeling?
M:Much better now that I began taking an antibiotic. Students Health gave me one, and it’s really help.You know that it amazes me that the human races survive before antibiotics.
W:I agree. When my father was a young boy in me 1940’s, he got blood poisoned and would have died.But his doctor had heard of this new drug, called penicillin.
M:Wow, he was really lucky. And now we have lots of antibiotics that kill bacteria.
W:Well, penicillin kills bacteria, but not all antibiotics do. Some just slow the bacteria down until ournormal immune defenses can finish the job. Tetracycline works that way.
M:Wow, how do you know all these?
W:My mother used to look up all our medicines, prescription and nonprescription. There are lots of booksaround. It’s interesting. What antibiotic are you taking?
M:I don’t remember. It’s on the bottle.I think I’ll take a new look at the label and drop by the library to see if they have any reference books on medicine.See you in lab tomorrow.