Before approaching the next subject I wish to avoid the reproach of departing from the rules of the inductive method by drawing conclusions from the complex to the simple; that is to say, in this case, by applying to the lower centres a conclusion drawn from the observation of the higher centres, instead of proceeding in the opposite way. I am obliged to proceed in this manner by the very nature of the problem which really cannot be treated any other way. As we have to deal with the subjectivity of central phenomena it is impossible to seek its conditions when we have no direct means of proving its presence or absence. Now in respect to the subordinate centres we are reduced exclusively to objective observation, which in no way can teach us anything of the subjectivity of the changes which take place in them; therefore, whatever conjectures we may make in regard to the consciousness or unconsciousness of the motor reactions furnished by the lower centres, they can have only a certain degree of probability when we study these reactions by the aid of what subjective observation teaches us relative to the consciousness or unconsciousness of the cortical centres. It is because they have not followed this method that writers disagree so completely as to the presence or absence of subjectivity in the sensori-motor centres, and especially in the spinal cord. Let us begin with the latter.