An authority, speaking of this standpoint concerning the question referred to, says: "We may discover the causes of storms or earthquakes, and when our knowledge of them is sufficiently advanced we may be able to predict them as successfully as astronomers predict eclipses, but there is little hope that we shall ever be able to control them. So it may be with sex; a complete understanding of the causes which determine it may not necessarily give us the power of producing one or the other sex at will, or even of predicting the sex in any given case. Whether we shall ever be able to influence the causes of sex-determination cannot as yet be foretold; at present, biologists are engaged in the less practical, but immensely interesting, problem, of discovering what those causes are." The second usage of the term, includes and embraces the idea of the voluntary determination or control of the sex of the future child, by means of certain methods or certain systems of treatment, etc. Of recent years, science has been devoting considerable attention to the question of whether or not man may not be able to produce any particular sex at will, by means of certain systems or methods of procedure. Many theories have been evolved, and many plans and methods have been advocated, often with the expenditure of much energy and enthusiasm on the part of the promulgators and their adherents. In this lesson there will be briefly presented to you the general consensus of modern thought on the subject, with a general outline of the favorite methods and systems advocated by the several schools of thought concerned in the investigation. Professor Doncaster, the well-known authority on the subject, says: "But little progress has been made in the direction of predicting the sex of any child, and, if possible, even less in artificially influencing the determination of its sex. When the general principles arrived at are borne in mind, it must be confessed that the prospects of our ever attaining this power of control or even of prediction are not very hopeful, but the possibility of it cannot be yet regarded as entirely excluded. The general conclusions arrived at are that sex is determined by a physiological condition of the embryonic cells, that this condition is induced, at least in the absence of disturbing causes, by the presence of a particular sex-chromosome. [A "chromosome" is a portion of the chromatin, or substance characteristic of the nucleus of the cell, this nucleus seemingly controlling the life-processes of the cell.] But there is evidence, which for the present at least cannot be neglected, that certain extraneous conditions acting on the egg or early embryo may perhaps be able to counteract the effect of sex chromosome.