The earliest use of the term 'Handshaking Lemma' that I can find on Google Books is from page 24 of Match - Volumes 6-8 published by Institut für Strahlenchemie im Max-Planck-Institut für Kohlenforschung in 1979 (https://books.google.com.ph/books?id=wPIsAQAAIAAJ).
Although the use of this result was already known to Euler, I'm interested in the coinage of the 'handshaking' name. An article by Hopkins and Wilson shows that Euler doesn't frame the bridges of Konigsberg problem in terms of handshakes (https://www.maa.org/sites/default/files/pdf/upload_library/22/Polya/hopkins.pdf).
What's the earliest recorded use of the name 'Handshaking lemma'?
EDIT: The earliest result from Google Scholar is a survey article by Wilson submitted in 1971 (https://www.tandfonline.com/doi/abs/10.1080/002073970003020). There are earlier references to the content of the handshaking lemma (see page 154 of the Bulletin of the Atomic Scientists - Apr 1958 https://books.google.com.ph/books?id=zgkAAAAAMBAJ) but I am only interested in the coinage of the term "handshaking lemma".