Early lab notes provide insights into Flexner's research in Asia. For example, an 1899-1900 diary offers a window into Manilla hospitals, travel by rickshaw in Tokyo, and observations on geisha, saki, kimonos, and Emperor in Japan. A later notebook, which purports to document a "Trip to China" in August 1915, actually features observations on the population of Honolulu, female education in Korea, and treatment of tuberculosis in Japan.
 
Later notebooks record Flexner's travels in Europe and final years as director of the Rockefeller Institute. A book misdated "January 3, 1931" provides an account of his journey to England and France to attend the Inter-Allied Scientific Conference (9/15-12/28/1918). Notably, on that trip, Flexner learns of the armistice from his waiter and wonders what the future will hold for Germany after the dissolution of Austria-Hungary (11/11/1918). Interspersed in later journals, researchers will discover Flexner's reflections on "Hitler & Jewish intellectuals" (4/12/1933) and the musings on the "German University Situation" (4/15/1933). In a notebook dated December 1934, Flexner documents a trip to Cairo (12/21/1934) and an encounter with FDR, Jr. (1/18/1935). Several notebooks document his directorship at the Rockefeller Institute between 1930-35, including the effects of the Great Depression on the Institute's budget (6/5/1932), encounters with Rockefeller family in (1931 and 1935), and his personal ambitions (1931).
 
Perhaps most surprising are a series of loosely-bound notes from 1938-1944. Those notes include a trip to England on the eve of World War II (1/1/1938-2/7/1939) as well as reflections on the outbreak and progress of the war. "England & France having exhausted every effort to influence Hitler declared war on Poland," he writes two days after Germany invades Poland, adding, "No enthusiasm on the part of any population—German, English, French—on [going late] this war as happened in 1914!" (9/3/1939). A year later, he records the German invasion of Paris, writing, "poor French, poor world civilization" (6/15/1940). Researchers interested in the history of World War II will discover that Flexner studiously records and comments upon key events, including Italy's entrance into the war (6/10/1940), FDR's declaration of a state of emergency (5/27-5/28/1941), the Japanese bombing of Pearl Harbor (12/7/1941), the U.S. declaration of war on Japan (12/8/1941), the surrender of Italy (9/4/1943), D-Day (6/6/1944), the liberation of Paris (8/23/1944), and FDR's landslide reelection to a fourth term (11/7/1944).

With 38 volumes spanning 1899-1944, the Simon Flexner Diaries (1899-1944) provide rich insights into Flexner's laboratory work, leadership at the Rockefeller Institute, study of pathology and bacteriology in the Philippines, and observations on Europe at the outbreak of World War II. Alongside his laboratory notes from Manila (1899-1900), early notebooks record medical and ethnographic observations from Japan (1900, 1915), Korea (1915), and Hawaii (1915), whereas later journals document his late-tenure as director of the Rockefeller Institute (1930-35), travels in colonial Egypt (1934), and visit to France (1918, 1931) and England (1918, 1931, 1938-39) in the years between World War I and World War II. The diaries contained in the Simon Flexner Papers ought to interest scholars researching twentieth-century medicine, philanthropy, colonialism, and war, as well as Flexner's leadership of the Rockefeller Institute and contributions to the fields of pathology and bacteriology.
 
Early lab notes provide insights into Flexner's research in Asia. For example, an 1899-1900 diary offers a window into Manilla hospitals, travel by rickshaw in Tokyo, and observations on geisha, saki, kimonos, and Emperor in Japan. A later notebook, which purports to document a "Trip to China" in August 1915, actually features observations on the population of Honolulu, female education in Korea, and treatment of tuberculosis in Japan.
 
Later notebooks record Flexner's travels in Europe and final years as director of the Rockefeller Institute. A book misdated "January 3, 1931" provides an account of his journey to England and France to attend the Inter-Allied Scientific Conference (9/15-12/28/1918). Notably, on that trip, Flexner learns of the armistice from his waiter and wonders what the future will hold for Germany after the dissolution of Austria-Hungary (11/11/1918). Interspersed in later journals, researchers will discover Flexner's reflections on "Hitler & Jewish intellectuals" (4/12/1933) and the musings on the "German University Situation" (4/15/1933). In a notebook dated December 1934, Flexner documents a trip to Cairo (12/21/1934) and an encounter with FDR, Jr. (1/18/1935). Several notebooks document his directorship at the Rockefeller Institute between 1930-35, including the effects of the Great Depression on the Institute's budget (6/5/1932), encounters with Rockefeller family in (1931 and 1935), and his personal ambitions (1931).
 
Perhaps most surprising are a series of loosely-bound notes from 1938-1944. Those notes include a trip to England on the eve of World War II (1/1/1938-2/7/1939) as well as reflections on the outbreak and progress of the war. "England & France having exhausted every effort to influence Hitler declared war on Poland," he writes two days after Germany invades Poland, adding, "No enthusiasm on the part of any population—German, English, French—on [going late] this war as happened in 1914!" (9/3/1939). A year later, he records the German invasion of Paris, writing, "poor French, poor world civilization" (6/15/1940). Researchers interested in the history of World War II will discover that Flexner studiously records and comments upon key events, including Italy's entrance into the war (6/10/1940), FDR's declaration of a state of emergency (5/27-5/28/1941), the Japanese bombing of Pearl Harbor (12/7/1941), the U.S. declaration of war on Japan (12/8/1941), the surrender of Italy (9/4/1943), D-Day (6/6/1944), the liberation of Paris (8/23/1944), and FDR's landslide reelection to a fourth term (11/7/1944).