investigation vs physiology

investigation

noun
  • The act of investigating; the process of inquiring into or following up; research, especially patient or thorough inquiry or examination 

physiology

noun
  • A branch of biology that deals with the functions and activities of life or of living matter (as organs, tissues, or cells) and of the physical and chemical phenomena involved. 

How often have the words investigation and physiology occurred in a corpus of books? (source: Google Ngram Viewer )