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Page from Sir Ronald Ross' notebook (1897)

The monsoon was late in 1897 and the heat intolerable. The sweat from the forehead and hands of Ronald Ross, a commissioned officer in the Madras branch of the Indian Medical Service, had begun to rust the screws of his microscope and his last remaining eyepiece had cracked in the heat.

Ross was busy dissecting mosquitoes in his “dark, hot little office” in the hospital at Begumpett yet he dared not cool down by using his ceiling fan or “punkah” because of the risk of it blowing away his feather-light, tiny quarry. All the while, he was tormented by swarms of “eye flies”, minute little insects that tried to get into his ears and under his eyelids, which flew into the room with the light entering under the eaves of the verandah.

It was mid-August and one of his assistants brought him some more mosquitoes that had been fed on a malaria patient called Husein Khan, who had been paid for the discomfort of being bitten deliberately. After several failed attempts, Ross finally found something unusual in the stomach of two of the mosquitoes.

“…I saw a clear and almost perfectly circular outline before me of about 12 microns diameter. The outline was much too sharp, the cell too small to be an ordinary stomach-cell of a mosquito. I looked a little further. Here was another, and another exactly similar cell,” he later wrote. 

In the laboratory notebook he used at the time he called these circular entities “pigmented bodies”, which he drew in loving detail. They were later identified as malaria parasites, and Ross was the first person to see them inside a mosquito’s intestinal tract.

It took him 10 days to write a paper on his discovery, entitled “On some peculiar pigmented cells found in two mosquitoes fed on malarial blood.” It was eventually published in the British Medical Journal in December 1897, and in 1902 Ross was awarded the Nobel Prize in Medicine, the first Briton to win it. 

Ross had effectively discovered the malarial parasite in the gut of a mosquito and had been vindicated for his theory that the disease was transmitted when female insects fed on a diet of human blood. As Ross had hypothesised a year earlier: “The belief is growing on me that the disease is communicated by the bite of a mosquito…She always injects a small quantity of fluid with her bite – what if the parasites get into the system in this manner?”

Of course, knowing how malaria was transmitted led to a way of controlling it. As Ross himself had pointed out in 1883, four years prior to his famous discovery, life would be a lot more pleasant and mosquito free if there were no water containers left lying around outside where the insects could breed – a suggestion that was met with some derision by his fellow officers.