In 1926, Kluyver and Hendrick Jean Louis Donker published the now classic paper, "Die Einheit in der Biochemie" ("Unity in Biochemistry"). The paper helped establish Kluyver's vision that, at a biochemical level, all organisms are unified. Kluyver famously expressed the idea with the aphorism: "From elephant to butyric acid bacterium – it is all the same". The paper, and other work from Kluyver's lab, helped support both the concept of biochemical unity as well as the idea of "comparative biochemistry", which Kluyver envisioned as biochemically equivalent to
comparative anatomy. The concept established a theoretical basis for studying chemical processes in bacteria and extrapolating those processes to higher organisms. The concepts of "biochemical unity" and "comparative biochemistry" were both very influential and probably Kluyver's most significant work. Kluyver's best known student,
C. B. van Niel, commented on his mentor's scientific influence and noted that by the middle of the 20th century, his work on biochemical unity was no longer cited. His aphorism was sufficiently widespread that in 1961
François Jacob and
Jacques Monod paraphrased it, without mentioning Kluyver, as "that old axiom 'what is true for bacteria is also true for elephants'" to justify the
genetic code's universality. His career was profoundly influenced by
World War II and the Nazi occupation of the Netherlands. ==Awards and honours==