Abstract: A method for analyzing the polypeptide content of animal tissue is described. The method includes the steps of (a) providing an animal tissue specimen; (b) depositing one or more portions of a hydrogel mixture including a protease on spatially discrete portions of the animal tissue specimen; (c) allowing sufficient time to pass for animal tissue under the hydrogel mixture to be form a digested mixture of animal tissue and hydrogel mixture; (d) removing the digested mixture from the animal tissue and extracting the polypeptides from the digested mixture to provide an extract; and (e) analyzing the polypeptide content of the extract by mass spectrometry.