In the late nineteenth century, the understanding of disease and disease transmission made huge strides, with a number of critical pathogens identified. However, certain diseases remained a complete mystery to medical science. At the dawn of the twentieth century, the understanding of yellow fever, known colloquially as “yellow jack” , became a priority for the US military when, during the Cuban leg of the Spanish-American war, more than five times as many soldiers died of disease than were killed in action: the War Department had scheduled its campaign for summer, when the risk of yellow fever was the greatest. When the Spanish sued for peace in the middle of July of 1898, those servicemen free of disease were shipped back to the US; but an occupying army of 50,000 remained in Cuba and at high risk. George Miller Sternberg, the army’s Surgeon-General, was a bacteriologist and a follower of Louis Pasteur and Robert Koch. He initially believed that yellow fever was the result of poor hygiene, and ordered Havana “sanitised”: garbage and sewerage dumps were removed from inhabited areas, and residences thoroughly cleaned. Ironically, these steps had the effect of reducing the incidence of almost every endemic disease but yellow fever. Although his measures failed to prevent the epidemic of 1898, Sternberg’s meticulous observations and records would provide an invaluable resource to those who took up the yellow fever challenge.

When a second epidemic struck in the summer of 1899, Sternberg and the Governor-General of Cuba, Leonard Wood – who had entered the army as a surgeon – appointed a team of medical researchers to tackle the problem of yellow fever, under the direction of Major Walter Reed. Reed and his colleague James Carroll, who was also appointed, had entered the yellow fever debate when their research, conducted at the Columbian University (later the George Washington University), disproved the prevailing theory of bacterial transmission. In June of 1900, Reed, Carroll, Aristides Agramonte and Jesse Lazear began their work. While confirming Sternberg’s negative observations, the team was struck by the erratic and illogical way that yellow fever outbreaks occurred: one man in a group might contract it, for instance. The idea finally dawned of a disease vector that could make choices – namely, the mosquito.

Disease transmission by insect was a very new concept; or at least, the proving of it was. A few years earlier, the deer tick had been confirmed as the means of transmission of babesiosis, or Texas cattle fever; but that (as far as they then knew) did not affect people. Meanwhile, the research of Ronald Ross, a British army surgeon and a disciple of Patrick Manson, the “father of tropical medicine”, had implicated the mosquito in the spread of malaria (a theory that Walter Reed had earlier rejected); Ross would later receive the Nobel Prize for his work. In following what they thought was a new line of inquiry, Reed and his people found that it was anything but: the idea of the mosquito being the yellow fever vector was at least fifty years old; while almost twenty years earlier, in Cuba, Dr Carlos Finlay, who along with George Sternberg had been part of the US Yellow Fever Commission of 1879, had not only declared his belief in the theory, but claimed to have identified the species of mosquito responsible. He was unable to prove it, however, and his assertions were met with ridicule and abuse. Belatedly becoming aware of Finlay’s work, Walter Reed sought him out, and learned of his conviction that the species Stegomyia aegypti – later, amidst much controversy, re-named Aedes aegypti – was the carrier of yellow fever.

While yellow fever is transmitted by mosquito, it is caused by a virus. If the blood taken up by a feeding mosquito contains the virus at a sufficient concentration, the virions can infect the epithelial cells of the insect and replicate within them, finally passing through the haemocoel to the salivary glands. There is thus a specific time-frame involved in transmission of the disease: mosquitoes only receive sufficient virus if they feed during the first few days of illness, when the viral load is high, and cannot transmit the disease until nearly a fortnight later. It was Finlay’s inability to grasp this, and his consequent failure to design appropriate protocols, that derailed his experiments.

It was therefore up to Reed’s team to do what Finlay had earlier failed to do: they had to design a series of experiments that would prove conclusively that yellow fever was transmitted by mosquito. Of course, designing the experiments was one thing; carrying them out was another. What the commission needed was human test subjects....

All in all, one would think, the yellow fever story was unlikely material for a Hollywood film – and an MGM film, at that. However, Warners had received much critical and social acclaim – and, probably more to the point, three Academy Awards – for The Story Of Louis Pasteur; and here was a chance to tell a similar story where the heroes were American! Yellow Jack was based upon a play by Sidney Howard, in turn derived from Paul De Kruif’s 1926 publication Microbe Hunters, which gives a detailed account of much of the work to which I have alluded. (Not to everyone’s satisfaction: Ronald Ross was so affronted by De Kruif’s description of him that he threatened to sue; that section of the book was subsequently omitted from British editions.) Howard’s play was not particularly successful – although a young actor called James Stewart, in the role taken by Robert Montgomery in the film, made enough of an impression to be offered a contract by MGM – but it offered the material needed for a “socially conscious” film. Nevertheless, Yellow Jack is a fairly half-hearted affair, with threadbare production values; if you didn’t know, you would never recognise this as an MGM film. You get the feeling that Louis B. Mayer’s desire for pats on the back (and Oscars) was very much outweighed by his distaste for the subject matter.

Nor is it surprising to find that the story has been somewhat cleaned up, romanticised and re-focussed. Although Walter Reed (Lewis Stone), James Carroll (Stanley Ridges), Aristides Agramonte (Frank Puglia) and Jesse Lazear (Henry Hull) play important roles – as well they should!! – the film chooses to take the usual movie tack of concentrating upon some ordinary joes, in this case five soldiers attached to the medical corps: Breen (William Henry), Brinkerhof (Alan Curtis), Busch (Sam Levene), “Jellybeans” (Buddy Ebsen) and their sergeant, John O’Hara (top-billed Robert Montgomery, complete with a grating Irish brogue). Inasmuch as these five men will eventually volunteer to be Reed’s test subjects, the shift isn’t entirely unjustified; but you nevertheless get the feeling that the producers didn’t want to risk boring the audience with too much of that “science” stuff. This crew is, of course, the usual cross-cultural menagerie – with Ebsen’s “slow Southerner” routine being particularly annoying. However, one real point of interest here is the behaviour of Busch, who is not only reading Karl Marx, but spouts Communist doctrine at the drop of a hat, besides bemoaning the fact that he can’t be in Chicago to “help the Movement”. Astonishingly, he does all this with impunity: his tent-mates get irritated with his habit of turning everything into a political debate, but they voice no objection to his beliefs. This is another startling thing to find in an MGM film – and would have been unthinkable a year or so later.

The breakthrough in the yellow fever research comes when a young soldier collapses on his way to the dock to ship out. It is determined that he spent the preceding month in the guardhouse, sharing communal meals and water and living in close quarters with eight others, none of whom have the disease. It is these circumstances, which offer a practical repudiation of most of the theories of disease transmission, that lead Major Reed to contemplate the mosquito. Agramonte then unearths a monograph by Dr Carlos Finlay (Charles Coburn, doing a thick Scottish accent, even though Finlay was born and bred in Cuba), presented nineteen years earlier at a medical conference – where his theory was rejected with scorn and laughter. Reed and his people track down Finlay who, after some persuasion and expression of hurt feelings, gives them his isolated specimens of Stegomyia aegypti, and some dried S. aegypti eggs. The team is then ready to commence its experiments; all it needs is some subjects.

(Although Walter Reed and his people are generally credited for the discovery of yellow fever’s transmission vector, Reed himself was always adamant that all credit should go to Finlay.)

In its efforts to create more drama – which personally I wouldn’t have thought were necessary – the screenplay of Yellow Jack takes a number of liberties with the truth. Perhaps the oddest is its depiction of James Carroll as a rough-mannered defeatist, who spends the first part of the film trying to convince Walter Reed to quit and go home. The greatest deviation, however, is the film’s insistence that Reed had great trouble getting any volunteers for his experiments. This is a fabrication. James Carroll himself was amongst those who allowed himself to be bitten by infected mosquitoes; he survived, although with severe damage to his health; while Jesse Lazear died of yellow fever. It has never been determined whether Lazear’s death was an accident, or whether he infected himself deliberately but kept it secret, to ensure that the insurance that was to support his family would be paid. Meanwhile, quite a number of soldiers also volunteered for the program, most of them under the pragmatic assumption that, being stationed in Cuba, they were probably going to get yellow fever anyway, so why not do it in a good cause?

Yellow Jack, however, chooses to give us a scene where the dying Jesse Lazear moans, “A whole army of men, and not one volunteer!” It is Lazear’s death (portrayed as an accident) that convinces O’Hara and his men – and only them – to raise their hands. The depiction of Reed’s experiments is the most accurate and the most interesting part of the film. Three of the men, Busch, Breen and “Jellybeans”, are confined for three weeks to a specially-built cabin under conditions theorised to promote the contraction of yellow fever. Their environment is heated; they share their food and drink; and they are provided with the clothing and bedding of men who died of the disease.

(Not surprisingly, Yellow Jack makes no reference to, let alone depicts, yellow fever’s most notorious manifestation: bloody projectile vomiting. However, Reed does tell the men that their cottage will be made, “As filthy as possible with the by-products of yellow fever”, which is a strong enough line for an MGM film of 1938, plus an uncomfortable mental image for anyone familiar with the disease.)

Meanwhile, Brinkerhof and O’Hara are confined in the second cabin; Brinkerhof is bitten by a carrier mosquito, O’Hara is not. Of the five men in the experiment, Brinkerhof alone contracts the disease. However, there still remains the question of O’Hara’s possible immunity to the disease – so he returns a second time to the cottage, and allows himself to be bitten also. His illness is a serious one, but he recovers; and we cut to the sight of the soldiers attached to the medical corps eradicating from Havana all possible Stegomyia breeding grounds – although there is no mention of the fact that that the real occupying forces had to impose martial law to get the job done! The operation is successful, and the historical portion of the story concludes with the departure of Major William Crawford Gorgas (Henry O’Neill), who has been hovering on the fringe of the story throughout, for Panama – where he intends to build a canal....

While all this is reasonably accurate, and laudable, I find it disappointing that Yellow Jack omits one of the most important moments in its story – probably because none of its authors realised at the time just how important it was. The film has Walter Reed giving a brief verbal explanation of the experiments to his volunteers. Actually, Reed prepared significant documentation for each man, in which he spelled out the theory behind the experiments, what they hoped to prove, and how they intended to prove it. The very real risk of death was made explicit, but so was the greater chance for survival, since treatment would commence the moment any symptoms showed. In short, it was Walter Reed who developed the concept of informed consent, which today is the fundamental principle underlying all human-based medical research – although it would take many decades, and far too many instances of unethical experimentation, before it became so. (In fact, during 1956 and 1957, the US Army secretly released mosquitoes carrying yellow fever and dengue fever in Georgia and Florida, to investigate their potential as biological weapons.)

The triumph of Walter Reed and his volunteers is not the story end of Yellow Jack, unfortunately. One of the re-shapings done when the play was adapted was to bring Robert Montgomery’s character to the forefront, and to create a completely unnecessary love interest for John O’Hara in the form of army nurse Frances Blake (Virginia Bruce). Far too much of the film is given over to their relationship, in which we suffer through yet another movie example of a serious, dedicated, professional woman being badgered into neglecting her work in favour of “moonlight” and “a walk on the beach”. This is exasperating enough in its own right, but all the more so for another who knows the true history behind Yellow Jack, which neglects to so much as mention Nurse Clara Maass.

Clara Maas was an American nurse who volunteered for military duty, acquiring expertise in tropical medicine through service in Cuba and the Philippines; she was invalided home from the latter after contracting dengue fever. Recovering, she then returned to Cuba at the request of Major Gorgas, and was attached to Walter Reed’s Commission. She was one of those who volunteered to be bitten by an infected mosquito, and contracted yellow fever as a consequence. She survived it, however; and later volunteered herself again. The sometimes erratic nature of yellow fever had led to the theory that survival of the disease automatically conferred subsequent immunity. The theory was incorrect: Clara Maass, intentionally infected for a second time, died in August of 1901, and was buried with full military honours.