For example, the backs of the hands and of the feet, or the palms and soles, are often not only symmetrically, but similarly, affected with psoriasis.

So are the elbows and the knees; and similar portions of the thighs and the arms may be found affected with ichthyosis.
Sometimes also specimens of fatty and earthy deposits in the arteries occur, in which exact similarity is shown in the plan, though not in the degree, with which the disease affects severally the humeral and femoral, the radial and peroneal, the ulnar and posterior tibial arteries." Dr.William Budd[192] gives numerous instances of symmetry in disease, both lateral and serial.

Thus, amongst others, we have one case (William Godfrey), in which the hands and feet were distorted.

"The distortion of the right hand is greater than that of the left, of the right foot greater than that of the left foot." In another (Elizabeth Alford) lepra affected the extensor surfaces of the thoracic and pelvic limbs.

Again, in the case of skin disease illustrated in Plate III., "The analogy between the {184} elbows and knees is clearly expressed in the fact that these were the only parts affected with the disease."[193] Professor Burt Wilder,[194] in his paper on "Pathological Polarities," strongly supports the philosophical importance of these peculiar relations, adding arguments in favour of antero-posterior homologies, which it is here unnecessary to discuss, enough having been said, it is believed, to thoroughly demonstrate the existence of these deep internal relations which are named lateral and serial homologies.
What explanation can be offered of these phenomena?
To say that they exhibit a "nutritional relation" brought about by a "balancing of forces" is merely to give a new denomination to the unexplained fact.