crabs vs tabes dorsalis

crabs

noun
  • pubic lice 

tabes dorsalis

noun
  • tabes of the back; a degeneration of the sensory neurons of the spinal cord carrying afferent information. 

  • neurosyphilis in the form of such degeneration. 

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