The second period of Giaja’s work actually started with his return to Belgrade after WWI and lasted over 20 years. In this period, his research interest became more focused on bioenergetics and the relationship between metabolism, temperature and asphyxia, and definitely led him to intense studies on hypothermia and its practical use. The work from this period was compiled in Giaja’s seminal two-volume monograph “Homeothermia and thermoregulation” (Giaja, 1938a,b), in which he published his classical curve of thermoregulation (“Djaja’s diagram”).

The Diagram on Thermoregulation by Jean Giaja (Giaja, 1938). This diagram is now called Giaja’s Diagram.
Reference:
Andjus PR, Stojilkovic SS, Cvijic G. Ivan Djaja (Jean Giaja) and the Belgrade School of Physiology. Physiol Res. 2011;60 Suppl 1:S1-13. Epub 2011 Jul 19. [link]