Editing Robert Koch (section)

=== Acquired immunity ===
Koch observed the phenomenon of acquired [[immunity (medical)|immunity]]. On 26 December 1900, he arrived as part of an expedition to [[German New Guinea]], which was then a protectorate of the German Reich. Koch serially examined the [[Indigenous people of New Guinea|Papuan people]], the indigenous inhabitants, and their blood samples and noticed they contained ''[[Plasmodium]]'' parasites, the cause of [[malaria]], but their bouts of malaria were mild or could not even be noticed, i.e. were [[subclinical]]. On the contrary, German settlers and Chinese workers, who had been brought to New Guinea, fell sick immediately. The longer they had stayed in the country, however, the more they too seemed to develop a resistance against it.<ref>{{lang|de|Hugo Kronecker: Hygienische Topographie}} In: A. Pfeiffer (Editor): {{lang|de|21. Jahresbericht über die Fortschritte und Leistungen auf dem Gebiete der Hygiene.}} 1903. Publisher: Friedrich Vieweg und Sohn, Braunschweig, 1905. p. 68</ref>