It has scarcely been possible in recent years to open a newspaper without our eye being arrested by head-lines telling us of racial strifes or international contentions. One day we read of race riots; on the next we learn that the inhabitants of a certain area of land demand separation from all surrounding peoples. By a process of 'self-determination' they demand to be recognized as a separate people or nation. These racial and national contentions are not restricted to any particular people or land; we find them in every country. The politician is too near to these racial and national manifestations of the modern world to see them in their proper light; even the historian is not far enough away from them to see them in their right perspective. You cannot explore the secret sources from which they spring unless you have grasped the immensity of man's unwritten history. Let me make my meaning quite clear by an historical example chosen from man's body. Among our modern populations there are no ailments more prevalent than those which arise from a disordered working of the great bowel. Why this part of our bodily machinery should fail us under modern conditions of diet becomes quite apparent when we survey the history of man's distant past. For the anthropologist there are only two well-marked phases in human history. The first phase is that of Natural subsistence--an infinitely long and monotonous chapter, stretching over a million of years or more. The second is the phase of Artificial subsistence--a short chapter covering a period of 10,000 or 12,000 years at the utmost, but a period crowded with events which have a critical bearing on our present and future welfare. In the first or long phase mankind was broken into small and scattered groups which gained as best they could a sparse, uncertain, and coarse sustenance from the natural produce of shore and stream, moorland and woodland. In the second or short phase man conquered nature; by means of cultivation and domestication he forced from the soil a sure and abundant supply of food, thus rendering possible the existence of our modern massed populations. Now the machinery of man's body and the instinctive outfit of his brain, which had been evolved to answer to the conditions of life presented by the first long phase of his history, were also those which had to serve him when he entered the new conditions of the short or modern phase. We need not be surprised to find, then, that part of his ancient outfit is ill adapted to modern conditions of life. Man's great bowel, including the caecum, appendix, and colon, which answered his needs well when his dietary was coarse and uncooked, is ill contrived to deal with foods which are artificially prepared and highly concentrated. A school, which was headed by the late Professor Metchnikoff, even goes so far as to maintain that man would be improved by the complete removal of his great bowel--a doctrine with which I totally disagree.