Random endo-hydrolysis of N-acetyl-beta-D-glucosaminide (1->4)-beta-linkages in chitin and chitodextrins. Accumulates during senescence and in response to 3-amino-1,2,4-triazole (3-AT) and silver nitrate (PubMed:12947053). Induced by viral infection (e.g. cucumber mosaic cucumovirus, oil seed rape tobamovirus, turnip vein clearing tobamovirus, potato virus X potexvirus, and turnip mosaic potyvirus) (PubMed:12535341). Induced by pathogens (PubMed:12920300). Belongs to the glycosyl hydrolase 19 family. Chitinase class I subfamily.