Is there any difference in meaning

Q1. Is there any difference in meaning between "A majority of the students" and " The majority of the students"?

Q2. "Variolation the inhalation or transfer into superficial skin wounds of material from smallpox pustules had been practiced since at least the 1400s in the Middle East and China as a form of protection against that disease and was known to Jenner"

Is the phrase "transfer into superficial skin wounds of material from smallpox pustules" a correct structure? If so, what does "transfer into" mean here?