The Prevention of Malaria in the Federated Malay States, Preface by Ronald Ross (Liverpool: Liverpool School of Tropical Medicine, 1911), pp. 111, 121, 134

Apart from the evidence of the children, the history of the making of the railway which runs over the Pass, records severe malaria, especially at Ayer Kuning and Bukit Gantang, where large cuttings and a tunnel had been made. While the Malays native to Bukit Gantang who had acquired immunity in their childhood could live in the valley, the non-immune Tamils on the railway construction suffered severely. We often see Javanese who generally have acquired immunity in their childhood, living in places which Tamils have had to abandon.