A study of the plasticity of protoplasm offers all the difficulties of such a study on gelatin and those additional ones which are associated with a substance that is alive and can be had only in microscopic quantities. It is the task of the biologist to conquer, as best he can, these latter difficulties which have to do with method, but he must appeal to the chemist for help in the interpretation of results. Patient and sympathetic cooperation between chemist and biologist is necessary if physical biology is to advance.