Justine Olive Johnstone (Mrs. Walter Wanger; January 31, 1895 – September 4, 1982) was an American stage, and silent screen actress, turned pathologist.

[citation needed] When Johnstone's husband fell ill in 1927, his doctor, Samuel Hirschfeld, convinced her to enroll in science courses at Columbia University, where she studied plant research.

Their key breakthrough was to slow down the rate of delivery and avoid what was then known as "speed shock" by introducing the now-ubiquitous drip technique.

[6] Later, Johnstone and her husband moved to Los Angeles, where as a research assistant to physicians she studied cancer and helped develop the discipline of endocrinology.

[1][6] Justine Wanger died in Santa Monica, California from congestive heart failure, aged 87.