Even the qualification of “health” is not sufficient. A thoughtless person may say with the most invincible air, “Parents should, at any rate, be healthy,” but that alone is only a misleading vague formula for good intentions. In the first place, there is every reason to believe that transitory ill-health in the parent is of no consequence at all to the offspring. Neither does acquired constitutional ill-health necessarily transmit to a child; it may or it may not react upon the child’s nutrition and training, but that is a question to consider later. It is quite conceivable, it is highly probable, that there are hereditary forms of ill-health, and that they may be eliminated from the human lot by discreet and restrained pairing, but what they are and what are the specific conditions of their control we do not know. And furthermore, we are scarcely more certain that the condition of “perfect health” in one human being is the same as the similarly named condition in another, than we are that the beauty of one type is made up of the same essential elements as the beauty of another. Health is a balance, a balance of blood against nerve, of digestion against secretion, of heart against brain. A heart of perfect health and vigour put into the body of a perfectly healthy man who is built upon a slighter scale than that heart, will swiftly disorganize the entire fabric, and burst its way to a haemorrhage in lung perhaps, or brain, or wherever the slightest relative weakening permits. The “perfect” health of a negro may be a quite dissimilar system of reactions to the “perfect health” of a vigorous white; you may blend them only to create an ailing mass of physiological discords. “Health,” just as much as these other things, is, for this purpose of marriage diplomas and the like, a vague, unserviceable synthetic quality. It serves each one of us for our private and conversational needs, but in this question it is not hard enough and sharp--enough for the thing we want it to do. Brought to the service of this fine and complicated issue it breaks down altogether. We do not know enough. We have not analyzed enough nor penetrated enough. There is no science yet, worthy of the name, in any of these things. [Footnote: This idea of attempting to define the elements in inheritance, although it is absent from much contemporary discussion, was pretty evidently in mind in the very striking researches of the Abbé Mendel to which Mr. Bateson--with a certain intemperance of manner--has recently called attention. (Bateson, _Mendel’s Principles of Heredity_, Cambridge University Press, 1902.)]