This post is the fourth in an ongoing series about the history of the U.S. Army Yellow Fever Commission and the historical context of its work. The posts are and will become pages of a revamped online exhibit about the Commission. Some of the posts will contain content that has been previously published by the Claude Moore Health Sciences Library, while others will contain new content. The post preceding this one in the series is titled, Yellow Fever in the United States.
In the decades leading up to the formation of the U.S. Army Yellow Fever Commission, revolutionary developments in science and medicine would lay a foundation for the Commission’s groundbreaking work. The rise of the germ theory of disease spurred important investigations into the biological causes of yellow fever and improvements in research methodologies would yield increasingly accurate data about the nature of the disease. While the U.S. Army Commission has been rightfully recognized for their role in proving that mosquitoes were the vector for yellow fever, the experiments would not have been possible without the insights of other pioneers working at the end of the 19th century.
Some of the most significant yellow fever research of the late 19th century can be directly linked to an earlier committee known as the Havana Yellow Fever Commission. The U.S. National Board of Health formed the Commission in the wake of the 1878 yellow fever epidemic in the Mississippi River Valley.  Investigations by public health experts revealed that the devastating epidemic, like many other outbreaks in the United States, could be traced back to an infected ship that had arrived from Cuba. With this knowledge, the National Board reasoned that it would help prevent future epidemics by forming a commission that could investigate yellow fever in Cuba and recommend policies for preventing its spread from the island. 
The National Board recruited George Miller Sternberg of the U.S. Army, Stanford E. Chaillé of Tulane University, Juan Guitéras y Gener of Cuba, and T.S. Hardie of New Orleans to serve on the Havana Commission. With the full approval of the Spanish government in Cuba, the Commission conducted epidemiological and scientific investigations on the island in the Summer of 1879. The American delegation worked closely with another commission formed by the Spanish government for the express purpose of aiding the U.S.-led group and continuing its work after the Americans returned to the United States. 
The U.S. and Spanish Commissions did not discover the cause of yellow fever or how it was spread, but they did gather substantial data about the disease. Their scientific studies yielded new insights about the effects of yellow fever on the human body and confirmed that it does not affect many other species in the same way as it does humans.  Meanwhile, their epidemiological studies improved the scientific community’s understanding of the conditions in which yellow fever thrives.
Based on their experimental and epidemiological data, the Havana Commission recommended improvements for the U.S. quarantine system and advised the development of an extensive sanitation program in Cuba to prevent the spread of yellow fever. While the quarantine recommendations were generally sound, the call for sanitation improvements was based on an unverified assumption about the transmission of yellow fever. While the Commission admitted that “the whole truth has certainly not been fathomed” about the causes of yellow fever, they argued that there were significant correlations between the presence of unsanitary conditions and the prevalence of yellow fever in Cuba.  They incorrectly assumed that the elimination of these conditions through a large-scale public health program would likely halt the spread of yellow fever. This point was forcefully made in the Havana Commission’s report to the National Board of Health:
The people must be provided with means to become intelligent, enlightened, especially in hygiene, prosperous, and sufficiently numerous to eventually gain both the knowledge and the power necessary to correct their insanitary evils. This is not only the best, but the only means. Until their accomplishment (which the present generation will not live to witness) Havana will continue to be a source of constant danger to every vessel within its harbor, and to every southern port which these vessels may sail to during the warm season. 
Members of both the U.S. and Spanish commissions would continue their work after 1879 and become important figures in yellow fever research at the end of the 19th century. George Miller Sternberg, who was responsible for much of the biomedical research conducted by the U.S. commission, built upon his 1879 studies and continued the hunt for a biological cause of yellow fever.  At the same time in Cuba, a relatively-unknown physician from the Spanish commission, pursuing the vector for yellow fever, would recognize the critical link between yellow fever and the mosquito.
 In the years leading up to the 1878 epidemic there were fierce debates over the need for national quarantine laws and federal public health agencies. Proponents of national measures believed that public health measures could be more effectively implemented by a federal agency rather than the existing patchwork of local and state bodies. Opponents feared undue federal interference in policing powers that should be reserved for the states. The 1878 epidemic, which quickly spread from New Orleans to over 200 communities in 8 states, mobilized widespread support for national public health reform. In 1878 and 1879, Congress passed the National Quarantine Act and created the National Board of Health. The Board had a broad mandate to improve public health in the United States, but it proved to be short lived. With the memory of the 1878 epidemic fading, support for the National Board declined and states-rights advocates successfully lobbied to eliminate its funding in 1883. All of the powers that had been granted to the National Board were reassigned to the U.S. Marine Hospital Service. See: Duffy, John. The Sanitarians : a History of American Public Health. Urbana: University of Illinois Press, 1990. pp. 163-172.
 Annual Report of the National Board of Health. Washington: Government Printing Office, 1879. pg. 33.
 Ibid., pg. 35.
 Ibid. A report of the Commission’s examination of the blood in yellow fever is found on page 64 while a report on its examination of the affects of yellow fever on animals is found on page 65.
 Ibid., pg. 46. Later in the report, the Havana Commission argues that the following are the causes of unsanitary conditions in Cuban ports: tainted water supplies, inadequate drainage, unpaved streets, architectural flaws, and polluted harbors. See pp. 50-54.
 Ibid., pg. 54.
 Sternberg would emerge as the preeminent scientific expert on yellow fever in the United States and published many articles on the subject. In 1887, the U.S. Marine Hospital Service would commission Sternberg to conduct a multi-year scientific study on the disease. The resulting Report on the Etiology and Prevention of Yellow Fever was published in 1890 and records the results of Sternberg’s study including his failed attempts to find the microorganism that causes yellow fever. Despite having no strong scientific evidence to support his claims, Sternberg argued that the results of his study suggested that people are infected with yellow fever when they come in contact with the bodily fluids and excrement of others who carry the disease. See Sternberg, George Miller. Report On the Etiology and Prevention of Yellow Fever. Washington: Government Printing Office, 1890. pg. 223.