26. This digression on the native and acquired dispositions of the organism, while it has brought into strong light all that can be cited in favor of regarding animal bodies as mechanisms, and their actions as the direct consequences of mechanical adjustments, has also made conspicuous the radical difference between an organism and a machine. We cannot too emphatically insist on this radical difference. Between the group of conditions involved in the structure and action of a machine, and the group of conditions involved in the structure and action of an organism, there are contrasts as broad as any that can be named. To overlook these in taking account solely of the conditions common to both groups is a serious error. On such grounds we might insist that a tiger is a violet, because both are organisms. The biologist will admit that an organism is a mechanism, and (in so far as its bodily structure is concerned) a material mechanism. All the actions of this structure are therefore mechanical, in the two senses of the term: first, as being the actions of material adjustments; secondly, as being movements, and thereby included under the general laws of motion represented in Mechanics; the abstract laws of movement for an organic body are not different from the abstract laws of movement for an inorganic body. So far we have been considering the abstract relations only. No sooner do we consider the phenomena as concrete wholes, than we find great diversity in the modes of production of the movements in organisms and machines. Now it is precisely the modes of production which have interest for us. We never understand a phenomenon so as to gain any practical control over it, or any theoretical illumination from it, unless we have mastered some of its conditions; our knowledge of these conditions is the measure of our power. CHAPTER III. THE RELATION OF BODY AND MIND.