Manifestations of morbid heredity result not in inheritance of the whole defect but in disturbance of relations of structure and hence of function, producing, as Kiernan remarks, a constitutional deficiency which takes the line of least resistance. The extent and direction of this line of least resistance depend on the amount of healthy atavism which separate organs and structures of the body preserve. The line of least resistance sometimes taken is excellently illustrated in the occurrence of stigmata already pointed out in the case of epileptic guinea-pigs. This unilateral predisposition (which, as Kiernan has shown, is due usually to heredity or intra-uterine causes) may be artificially produced. Kasparek[88] cut one sciatic nerve of a guinea-pig and (after all inflammatory symptoms had subsided) injected the opposite ear with cultures of pus microbes. He killed the animal after some days. The sound side was found free from suppuration, but immense abscesses existed on the side of the cut nerve. Such local predisposition was pointed out by Merrill[89] over forty years ago. This condition occurs, as Féré has shown,[90] in many systemic and infectious diseases which presents a localisation due to heredity, or determined by anterior morbid state of the nervous symptom. Sometimes these manifestations are limited to the side free from nervous trouble. As a rule they attack the side which is the predominant seat of nervous symptoms. Féré points out that in chromatic iris asymmetry the iris (coloured part of the eye) is most coloured on the side most affected by arrest of development. Localisation of nervous trouble occurs on the side most affected by hare-lip. Heuse has observed the co-existence on the same side of congenital cataract and of deformities of the skull and chest. Hernia is often an expression of hereditary defect (Le Double) taking the unilateral line of least resistance. Testicle inflammations of microbic origin (venereal or otherwise) occur as a rule on the side where hernia is located in the groin. In one-sided malformations of ovary or testicle (decreased or increased in size, or changed in shape or location) microbe inflammation almost always occurs at the seat of the anomaly. This principle is illustrated in the experiments of Dupuy.[91] Here, while as a rule, the scions of guinea-pigs (rendered epileptic by section of the sciatic nerve) were epileptics and had deficient toes, still in some epilepsy resulted without the toe anomaly, while still more rarely the toe anomaly was present without the epilepsy.