The narrator is explaining the following to the reader in this sentence: C The doctor and the professor started to lose interest in the specimens.
What is being explained?
Considering the focus on loss of interest and the lack of emphasis on monetary value, option C is the most accurate explanation of what the narrator is explaining to the reader.
The medical doctor and the professor no longer considered the specimen as holding any academic or monetary value hence, their reason of losing interest in them. There was no need to continue to expend resources on these.