Sources

http://www.timetoast.com/timelines/medical-inventions-during-the-1920s
http://www.infoplease.com/ipa/A0932661.html
http://www.factmonster.com/ipka/A0932661.html
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3749764/
http://pediatrics.aappublications.org/content/112/2/e132.full