A condition is congenital when the person is born with it. There are some diseases which are manifestly present at birth, for the causation of which it is necessary to go back to the period of life in utero. Some of these are obviously due to the action of external forces, mechanical or other, but there are others in which the causation is quite obscure. Among those whose cause is clear may be cited congenital syphilis, which is always a manifestation of hereditary syphilis. In this case a morbid poison is propagated from the parent to the offspring, and acts on the latter while still unborn.

Many of the congenital diseases consist in Malformations of the body as a whole or in part. These occur during the course of development and growth of the body, and consist in errors of excess or defect in the formation or disposition of the tissues. Some of them can, without difficulty, be traced to the action of external forces on the fœtus. For example, a limb or part of one may be amputated in the uterus, and the person may be born with a corresponding defect, perhaps partly remedied by subsequent growth of the injured part. There are probably many congenital defects, which, if they could be traced back to their origin, would be found due to mechanical interference, but it is only in regard to a few of them that this can as yet be done. Such mechanical interference may be due to inflammation, producing adhesion of parts, and thus hindering their due expansion. It seems probable that inflammations play a considerable part in the causation of diseases in the uterus, and these inflammations will be due to the action of external forces just as are those of extra-uterine life.

In regard to congenital susceptibilities, these, again, may be divided into those tending towards defect on the one hand and excess •on the other. Persons are born, it may be, with certain of their tissues unduly weak and tending to decay. These tissues may give way and become the seat of disease as a result of the action of causes which in most persons would produce no such effect. It may even be that at a certain period of life they may degenerate without any apparent determining cause. Then, as opposed to this, people may be born with a tendency to great excess in the growth of certain parts of their tissues. The causation of Tumours or Morbid growths is very obscure, but we may say at least that obvious congenital conditions, such as soft warts or moles, are not infrequently the starting points ol tumours in later life. We may also infer that conditions equally congenital, but situated so as not to be visible, may be the starting point of other tumours, the susceptibility to which has existed from the beginning of life.

It will appear from what has gone before that congenital diseases are due to a variety of causes, and that they owe comparatively little to inheritance. All that the term means is that the child comes into the world with the disease existent. Congenital susceptibility, on the other hand, will be for the most part due to inheritance.