Robe Koch assistant advised him to use agar instead of gelatine for solidifying culture media for cultivation of bacteria as -
Gelatin melts at 24degC. REF:Textbook of Microbiology, Ananthanarayan, and Paniker. Page no.: 39
Agar has no more nutrition
Gelatin melts at 24degC
Gelatin is not easily available
Agar is cheaper
general microbiology