An effervescent solid composition of matter is provided, which comprises, as an active component, a substance selected from chitosan, its derivatives and salts thereof and a second component capable of releasing CO.sub.2 in an acidic environment. Also, methods for treatment of a mammal suffering from a dermal wound, or for prophylactic or wound-healing treatment of lactating animals prone to develop or suffering from mastitis, are provided. The methods comprise the steps of: a) admixing said effervescent solid composition of matter with an aqueous liquid to form a solution or suspension thereof; b) contacting said animals with said solution or suspension to provide such treatment.