Proteins	Low molecular weight chemicals
Animal	Excreta of rats, mice etc; locusts; grain mites
Vegetable	Grain, flours; latex; green coffee bean; isphagula; latex	Plicatic acid (from western red cedar), pinewood resin
Microbial	Harvest moulds, Bacillus subtilis enzymes (in detergents)	Antibiotics—eg. penicillins, cephalosporins
Mineral		Acid anhydrides, isocyanates, complex platinium salts, polyamines, reactive dyes