It was by quite a different path that the Heilbronn doctor, Mayer, arrived at his results. To escape from the narrowness of his South German home town, he went, while still a youth, as doctor to a Dutch ship sailing to Java. When in the tropics he treated a number of sailors by blood-letting, he observed that the venous blood was much nearer in colour to the paler arterial blood than was usual at home. This change in the colour he attributed to the diminished intensity of bodily combustion, due, he believed, to the higher temperature of the tropics.