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 the 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 our normal 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 books around. 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.