After he founded the Institute, Đaja began his experimental work, adopting the motto Nulla dies sine experimentum (Not one day without the experiment).
His entire scientific work can be divided into three phases.
In the first phase, which started in his student days and lasted up to World War I, he concentrated on the research of the endogenic enzymes or ferments, which are produced by the glands of digestive organs.
He created a more rational nomenclature of the enzymes than the ones previously used.

When he returned to Serbia in 1919, his second phase was centered on metabolism.
In this period, he published a physiology textbook in 1923, Fundamentals of physiology.
In preface, he wrote that “he arranged the subject matter based on one leading idea: that circulation of matter and energy is the basic phenomenon of life, and that all physiological functions are subordinated to it.”
He also researched bioenergetics and an effect of the temperature and asphyxia induced numbness on living organisms.
His major work from this phase is the two-volume Homeothermy and thermoregulation from 1938.

Đaja began to research hypothermia in 1935 and from 1940 it became the focal point of his scientific work.
He was especially interested in the ways it can be achieved.
With his treatise State similar to the winter sleep of the hibernators achieved in rat by the means of barometric depression, published on 15 January 1940, he began researching the physiology of the deeply cooled homeothermous organisms.
He was interested in thermogenesis, gas circulation in organisms, adaptation to cold, defense role of hypothermia and metabolism in deep hypothermia.
His results from this period have found a wide application in medical physiology.

Apart from pure chemical processes in the human body, he was interested in philosophical decoding of the complex functional plexus in the natural world in general.
Considering physiology as the branch of biology which synthesizes the entire knowledge of the science of life, Đaja aimed to present the philosophical interpretation of the nature of science, its foundations and future development.
He published his philosophical views in Following the footsteps of life and science in 1931 and Man and the inventive life in 1955.
He presented thesis on the origin of the biological inventive power, purposefulness of certain phenomena in the living world and discussed the concept of usefulness in biology.
He tried to comprehend the mechanics of life, chemistry and physical chemistry of the living organisms and to give a unifying scientific philosophical theory which would encompass physiology, evolution and genetics.

He was also known as the major popularizer of biology, but also of science and arts in general and was remembered as an excellent lecturer and teacher.
After he founded the Institute, Đaja began his experimental work, adopting the motto Nulla dies sine experimentum (Not one day without the experiment). His entire scientific work can be divided into three phases. In the first phase, which started in his student days and lasted up to World War I, he concentrated on the research of the endogenic enzymes or ferments, which are produced by the glands of digestive organs. He created a more rational nomenclature of the enzymes than the ones previously used.
When he returned to Serbia in 1919, his second phase was centered on metabolism. In this period, he published a physiology textbook in 1923, Fundamentals of physiology. In preface, he wrote that “he arranged the subject matter based on one leading idea: that circulation of matter and energy is the basic phenomenon of life, and that all physiological functions are subordinated to it.” He also researched bioenergetics and an effect of the temperature and asphyxia induced numbness on living organisms. His major work from this phase is the two-volume Homeothermy and thermoregulation from 1938.
Đaja began to research hypothermia in 1935 and from 1940 it became the focal point of his scientific work. He was especially interested in the ways it can be achieved. With his treatise State similar to the winter sleep of the hibernators achieved in rat by the means of barometric depression, published on 15 January 1940, he began researching the physiology of the deeply cooled homeothermous organisms. He was interested in thermogenesis, gas circulation in organisms, adaptation to cold, defense role of hypothermia and metabolism in deep hypothermia. His results from this period have found a wide application in medical physiology.
Apart from pure chemical processes in the human body, he was interested in philosophical decoding of the complex functional plexus in the natural world in general. Considering physiology as the branch of biology which synthesizes the entire knowledge of the science of life, Đaja aimed to present the philosophical interpretation of the nature of science, its foundations and future development. He published his philosophical views in Following the footsteps of life and science in 1931 and Man and the inventive life in 1955. He presented thesis on the origin of the biological inventive power, purposefulness of certain phenomena in the living world and discussed the concept of usefulness in biology. He tried to comprehend the mechanics of life, chemistry and physical chemistry of the living organisms and to give a unifying scientific philosophical theory which would encompass physiology, evolution and genetics.
He was also known as the major popularizer of biology, but also of science and arts in general and was remembered as an excellent lecturer and teacher.
Ivan Đaja