Conversation so far:
When did Jonas Salk start doing Polio research?
In 1948, Harry Weaver, the director of research at the National Foundation for Infantile Paralysis, contacted Salk.
What was the first part of his research?
He asked Salk to find out if there were more types of polio than the three then known, offering additional space, equipment and researchers.
Did he find out if there were more than three types?
CANNOTANSWER.

Question: What did he discover in his research?
Self-contained rewrite: What did Jonas Salk discover in his research on polio?