Here we are upon ground which is more or less in our own choice or control. It is impossible to alter germ-plasm; but it is not impossible to control the environment in which it exists. To these two groups of characters, the germinal and those acquired under stimulus, there is to be added the third group which we have mentioned on a previous page, namely, those that are usually termed variations. For example, one occasionally finds that one individual in a family, the parents of which, and the other members of which, are quite normal, may be born with six fingers instead of five. Similarly one of a family may have a variation in the direction of an extraordinary capacity for the acquisition of knowledge of certain types. Hence the genius in music, mathematics, memory, morality, and so forth. As we have seen, these variations are termed spontaneous, to express the fact that we are at present ignorant of the laws in accordance with which they arise, though, of course, it is understood that those laws must exist. We have now surveyed the whole field of the possible origin of the characters of an embryo, and these may be summed up in the following tabular statement. { A. Inborn Characters-- { (_a_) Inherited (growing under the stimulus of { nutriment). An Embryo is { (_b_) Variations. made up of { B. Acquired Characters, obtained { (_a_) By nutrition. { (_b_) By use. { (_c_) By injury. The differences in individuals with which we are also familiar, are due to the varying proportions of the characters in the above table, and the characters themselves are those which constitute all the possibilities for any given person. Should the reader doubt this, or be sceptical as to whether the whole of the making of a man is contained in the above simple scheme, it would not be difficult for him to convince himself that the statement is a true one. Let him put down this book and take a sheet of paper and a pencil. Rule the sheet of paper into three columns, and at the top of each column place a heading as follows: Inherited; Acquired; and Variations. Thus:-- +----------------+---------------+-----------------+ | Inherited. | Acquired. | Variations. | +----------------+---------------+-----------------+ | | | | | | | | | | | | +----------------+---------------+-----------------+