All these agencies have this trait in common, that their damaging effect is often felt by the offspring as well as the parent, and, in most cases, in a far higher degree. The common doctrine of hereditary disease implies the actual transmission of a specific form of disease fully developed,--or, at least, of a tendency to it that may or may not be developed. The range within which it operates is supposed to be the narrow limits covered by a single specific affection. Daily experience, however, shows that the deviation from the primitive type is limited only by some conditions of structure. Any pathological result may be expected, not incompatible with the structure of the organ. And thus it is that the cerebral affection which fell upon the parent is represented in one child by insanity, in another by idiocy, in another by epilepsy, in another by gross eccentricity, in another by moral perversities, in another by ill-balanced intellect,--each and all implying a brain more or less vitiated by the parental infirmity. There is nothing strange in all this diversity of result. In the healthy state, organic action proceeds with wonderful regularity and uniformity; but when controlled by the pathological element, all this is changed, although the change has its limits. This diversity in the results of hereditary transmission is as strictly according to law as the similarity of features exhibited by parent and child. No presumption against the fact can be derived from this quarter, and therefore, if well-authenticated, it must be admitted. Many a man, however, who admits the general fact, refuses to make the application where it has not been usually made. When mania occurs in two or three successive generations, nobody overlooks the hereditary element; but when the mania of the parent is followed by great inequalities of character, or strange impulses to criminal acts, then the effects of disease are straightway ignored, and we think only of moral liberty and free-will. It may be difficult, sometimes, to make the proper distinction between the effects of hereditary physical vitiation and those of bad education and strong temptations; but the difficulty is of the kind which stands in the way of all successful inquiry, to be overcome by patient and profound study.