SYMMETRY OF DISEASE: This subject has been most ably treated by Dr. W. Budd *, of Bristol. Those local diseases, the cause of which is in the blood, usually affect the solids of the body symmetrically. This can he often well observed in lepra, psoriasis, se condary syphilis, gout, and rheumatism, and in the eruption caused by taking the iodide of potassium. It is due, no doubt, to the symmetrical disposition of those tissues for which the morbid poisons have a peculiar affi nity. It proves, moreover, that there is more of peculiarity in certain parts of organs than what meets the eye, which peculiarity is sym For, though the tissue of all parts of a bone, for instance, shall be exactly the same,,it shall be diseased at a certain part only, and the disease shall be repeated in ex actly the same part of the corresponding bone of the opposite side. Connected with this is the observation made above, that the corre sponding points of both sides of the body are exactly of the same age — have reached a cer tain stage of development at exactly the same time. But the force of this observation in
explaining the symmetry of disease is consi derably weakened by another fact noticed by Dr. W. Budd, namely, that the diseases above named are apt also to localise themselves in parts that are serially homologous, or corre sponding in the upper or lower limbs, as the knee and elbow, wrist and ankle; for these parts, though homologous, are not of the same age. It is well known that the development of the upper and lower limbs does not pro.. teed pari passe. There is here, at least, some determining agency more mysterious than mere age. Still more curious and mysterious is the relation of the eruption called shingles to the bilateralism of the body. It often ex tends zone-like around one half, stopping exactly at the median line before and behind, and thus seemingly affording evidence of that individuality of one half of the body which was spoken of as a feasible opinion above.