EDUCATION OF THE SENSES 169
used has been greatly modified. I believe, however, that I have arrived at a selection of objects (which I do not here wish to speak of in the technical language of psychology as stimuli) representing the minimum necessary to a practical sense education.
These objects constitute the didactic system (or set of didactic materials) used by me. They are manufactured by the House of Labour of the Humanitarian Society at Milan.
A description of the objects will be given as the educational scope of each is explained. Here I shall limit myself to the setting forth of a few general considerations.
First. The difference in the reaction between deficient and normal children, in the presentation of didactic material made up of graded stimidi. This difference is plainly seen from the fact that the same didactic material used with deficients makes education possible, while with normal children it provohes auto-education.
This fact is one of the most interesting I have met with in all my experience, and it inspired and rendered possible the method of observation and liberty.
Let us suppose that we use our first object,— a block in which solid gRometric forms are set. Into corresponding holes in the block are set ten little wooden cylinders, the bases diminishing gradually about ten millimetres. The game consists in taking the cylinders out of their places, putting them on the table, mixing them, and then putting each one back in its own place. The aim is to educate the eye to the differential perception of dimensions.
With the deficient child, it would be necessary to begin with exercises in which the stimuli were much more