If we think of the Habermas’ call for the revival of “quintessential, integral mind” which according to him ruled Europe until the period of enlightenment which initiated the future predominance of the socialist thought, the life and works of an academician Ivan Djaja should have an honorary status. In addition to being one of the greatest Serbian scientists – a physiologist and biologist, the founder of the scientific physiology based on experiments and the founder of the internationally recognized “Belgrade School of Physiology”, a member the Serbian Academy of Sciences and the French Academy of Sciences and the winner of prestigious scientific acknowledgements – Ivan Djaja was a philosopher, writer, rector of the University of Belgrade, the first correspondent of Politika from abroad and a skilled flautist but also an open-minded person who freely expressed his attitudes and who was ready to bear the consequences for that in the country in which he didn’t have to live and which many a time hasn’t realized the importance of its renowned men.

Ivan Djaja was born in L'Havre in France. His father, Božidar, a Serb from Dubrovnik, who also wrote several novels, was a naval captain, and his mother, Delphine Depoa, was French. Several important figures originated from the notable Djaja family: Jovan Djaja, Ivan’s uncle, was a doctor of philosophy from Vienna who with Nikola Pasic founded the Serbian Radical Party. He was twice the Minister of Internal Affairs and he was the ambassador in Athens and Sofia, a writer, a journalist and a translator (for instance, he translated Tacitus, Hugo, Manconi etc.). Sinisa Djaja, his son, was a teacher at the University of Belgrade and one of the founders of the Faculty of Pharmacy and the Head of the Institute of Phramaceutical Technology (1939–1957).

Soon after his birth, Ivan Djaja and his family moved to Serbia where his father became the captain of the steamboat “Deligrad”. After he finished primary and secondary school, Ivan returned to France where he spent a year at the Lycée Corneille where he studied philosophy and in 1903 he enrolled at the Sorbonne. He graduated in natural sciences in 1905 and published his first scientific paper on amylolytic inactivation of the dialyzed pancreatic juice in 1906 at the age of 22 with two associates. This paper was followed by a series of studies published in the journal of the Paris Biological Society one of which was accepted by the journal of the French Academy of Sciences. During his studies, Djaja also spent some time working with Paul van Tieghem at the Muséum national d’Histoire naturelle. After that he spent five years with Professor Yves Delage at the Marine Station in Raskoff, one of the well-known experimenters, who with van Tieghem immensely influenced Djaja’s scientific and creative work. Djaja earned his PhD in 1909 after defending his thesis, “Study on ferments of glycosides and carbohydrates in mollusks and crustaceans” at the Sorbonne.

Although half French with a doctoral degree from the Sorbonne and important contacts in the scientific world, Djaja would have had a brilliant career in Europe. Having been motivated by the profound patriotism and the professional challenge of establishing a scientific system in the underdeveloped country, he returned to Serbia the following year and in 1910 as a young assistant professor of physiology at the School of Philosophy of the University of Belgrade he established the first Chair in Physiology in the Balkans and organized the first Serbian Institute for Physiology. He led this Institute for more than 40 years. This marks the beginning of the so-called golden period of Serbian physiology. Two years later he published his monograph entitled “Ferments and Physiology” which was awarded by the Serbian Royal Academy of Sciences and the successful management of the Institute was awarded with an internationally recognized name for this institution: “Belgrade School of Physiology”.

The fact that in 1955 the French Academy of Sciences elected Djaja an associate member in the Medical Department in place of the deceased Sir Alexander Fleming, the discoverer of penicillin, tells us how important Djaja’s work was. A year before that he had received the title of doctor honoris causa at the Sorbonne. Let’s stop here for a moment because it was Djaja’s admittance to the French Academy that was the occasion for a small diplomatic scandal that would remain indicative of a reception of this renowned Serbian scientist in his own country. Namely, the Yugoslav ambassador did not attend the reception at the French Academy of Sciences on the occasion of Djaja’s admittance as a corresponding member. Ivan Djaja was always honest with people regardless of their position. Always well-dressed, kind, noble and well-educated, an intellectual par excellence, having had a sense of irony and the advocate of brotherhood among people, he was a thorn in the flesh to he local authorities. That feature put him in danger at the time of the First World War which started while he was in Vienna where he was under constant surveillance. This charateristic of his came to light during the school year of 1934/35 when Djaja, as a rector of the University of Belgrade, and the students protesed against the police raid into the building of the University of Belgrade defending the autonomy of this institution and its students. When in 1945, after the testimony of his daughter Ivanka, they presented him to Tito “as a students’ mother and a red rector” because he protected the pro-Socialist youth, he said: “I protected them so that they could study and I considered their political rapture only youthful foolhardiness.

Djaja kept a sense of fine irony until later. At the banquet which was organized on the occasion of inauguration of the new Minister of Education, Mrs Mitra Mitrovic, Milovan Djilas’s wife, he said: “I salute you as a person who came to the position which in this country belonged to St. Sava and Dositej Obradovic!” Understandably, the same moment he was proclaimed unsuitable and reactionary. Be that as it may, the freedom of speech for this great man remained an axiom. Therefore, he didn’t refrain from opposing the initiative that Josip Broz would become an academician because that would have been, as he used to say, the restoration of monarchy which would have ended in Tito becoming an honorary citizen of every single town in the country. Withal, to return to the beginning of this digression, on the occasion of the Yugoslav ambassador’s absence, Djaja said: “He should have come, I criticize my country only when I am in it.”

However, a good word about Djaja spread far across the borders of his country. Today scientists agree that Djaja’s scientific career could be distinguished by three periods devoted to three main topics: enzymes, metabolism and hypothermia. The first, the earliest period of his career, is crowned with a new rationale for a nomenclature of enzymes and the making of an apparatus for the measurement of oxygen (Djaja’s apparatus). The pick of the second period was Djaja’s seminal two-volume monograph “Homeothermia and thermoregulation” in which he published his classical curve of thermoregulation (“Djaja’s diagram”). In the fruitful part of the third period he established the so-called “Djaja’s Method”, i.e. hypothermia by confinement. Today, these professional contributions are widely applicative.

Djaja devoted a large part of his professional life to the popularization of science and healthy lifestyle and to writing philosophical books (the most important one of which was published in France entitled “Man and Inventive Life”). He was a great friend of Milutin Milankovic and a man at whose suggestion the Serbian Academy of Sciences changed its name into Serbian Academy of Sciences and Art. When in 2010 the Faculty of Biology organized a symposium “100th Anniversary of the Ivan Djaja’s Belgrade School of Physiology” in honor of Ivan Djaja, many of the world famous scientists accepted the invitation. This has just confirmed his importance and given rise to a thought which should be a priority to all of us today. Namely, we hear a lot about Tesla or Pupin who could only become famous outside their home country. They certainly deserve it. However, in the global challenges of the humankind it is necessary that we in Serbia have as many followers of Djaja’s legacy as possible both in the field of physiology and in the overall presentation of our country because Ivan Djaja is the evidence that one can leave a global scientific trace even in a small country like Serbia.