In the experiment, an extract from bacterial cells that could make protein even when no intact living cells were present was prepared. Adding an artificial form of RNA, polyuridylic acid, to this extract caused it to make an unnatural protein composed entirely of the amino acid phenylalanine. This showed that RNA controlled the production of specific types of protein. The importance of the break-through-work of Heinrich Matthaei was outlined by Hans-Jörg Rheinberger. In his book "Experimentalsysteme - Eine Geschichte der Proteinsynthese im Reagenzglas" the experimental work is shown in the worldwide rallye of biochemists. The book is published at WALLSTEIN ISBN 3-89244-454-4 see:Toward a History of Epistemic Things Synthesizing Proteins in the Test Tube- Hans-Jörg Rheinberger