"there will not be enough trees on the isthmus to make crosses for the graves of your labourers".
Disease was the biggest factor in the French failure. It would have been equally disastrous for the US venture, but for the efforts of four men.
The consensus in the 1890s was that malaria was carried by airborne germs, and that outbreaks in Panama were caused by the release of tainted air ("miasma") from the canal excavations. Yellow fever, they thought, was a disease caused by filth, especially human filth, that could only be defeated by good sanitation.
In fact, both diseases were carried by mosquitoes, as had been proved by British doctor Ronald Ross, in India; and the Cuban Carlos Juan Finlay and USArmy doctor Walter Reed, both working in Havana. They named the culprits: mosquito Anopheles is the sole carrier of malaria, and Stegomyia fasciata the carrier of yellow fever. In both cases, only the female bites humans.
There was no cure for either disease. The symptoms of malaria could be assuaged by taking quinine. Yellow fever was fatal in about 50 per cent of cases: those who survived it were immune.
Such immunity was enjoyed by another US Army doctor, William Gorgas (right), who took it on himself to convert the findings into all-out war on mosquitoes in Panama. He knew that mosquitoes breed in standing water and set about eliminating every potential breeding ground. Not even holy water stoops in the cathedral escaped his attentions. Ditches and swamps were sprayed with crude oil, buildings were fumigated, windows sealed or screened.
Dr Gorgas faced an even bigger enemy, however, the complacency and ignorance of his bosses, who would not be convinced of the urgent need to extend anti-mosquito operations well before the arrival of upwards of 30,000 canal labourers. He put his career and health on the line to prevail with his work. By 1905 yellow fever was virtually eradicated from Panama and malaria was in check. Dr Gorgas's work saved the canal project and the lives of thousands of workers - and produced a template for controlling the diseases worldwide.