But on carefully considering the facts, certain phenomena of profound meaning may strike us. Here, in a part of the body where no such tissues ordinarily exist and to which no such structures are ordinarily appropriate, there arise tissues and structures adapted to the physical circumstances imposed on that part. Out of what do these abnormal but appropriate tissues arise? The substances around--osseous, cartilaginous, membranous--consist of differentiated elements too far specialized to allow of transformation. These new tissues, then, must originate from the undifferentiated protoplasm pervading the part. The units of this protoplasm, subject to the actions proper to an articulation, begin to assume the appropriate histological traits--are determined by local stimuli to form tissues ordinarily associated with such stimuli. What is the inevitable implication? These units--physiological or constitutional, as we may call them--must have possessed latent potentialities of falling into these special arrangements under stress of such conditions. At one point there arises periosteum and at another ligamentous tissue, while for the shaping of the ends of the bones--here into a rude hinged form and there into a rude ball-and-socket form, according to the habitual movements--there goes on some appropriate deposit of bone. Hence we must conclude that in the units of protoplasm which have not yet been organized into special tissues, there resides the ability to take on one or other type of histological structure according to circumstances; and, further, that there resides in each of them the still more marvellous ability to co-operate with kindred units dispersed around in developing that arrangement of the parts required to constitute a “false joint.” So that while these units have a general proclivity towards the structure of the organism as a whole, they have also proclivities towards structures proper to the local conditions into which they fall. There is latent in each unit the constitution of the entire organism and by implication the constitution of every organ; and each unit while co-operating with the aggregate is ready to take part in that particular arrangement proper to the position it has fallen into. If the reader will refer back to §§ 97_d_, 97_e_, in which it is shown that each member of a human society possesses a combination of potentialities like these, he will be the better enabled to believe that this thing _may be_ so while he is unable to conceive how it _is_ so.