Letter from Otto Bier, Instituto Biologico (Brazil) to Michael Heidelberger

In this letter Otto Bier, one of Heidelberger's former postdoctoral students, illustrated how World War II affected scientific research, in this case in Brazil. Bier also reported results of his research on complement, a complex system of over twenty serum proteins that play an essential enzymatic role in host defense mechanisms against invading organisms. Heidelberger became one of the founders of the study of complement when he showed during the 1940s that it was a group of specific chemical substances.