Feature Test Devised for Measuring Efficiency of the Heart Share this: Share via email (Opens in new window) Email Click to share on Facebook (Opens in new window) Facebook Click to share on Reddit (Opens in new window) Reddit Click to share on X (Opens in new window) X Click to print (Opens in new window) Print By Science News Magazine Issue: Vol. 19 No. #521, April 4, 1931 Having trouble viewing this? Open in a new window