Malignant tumours seem to display a predilection for this region of the digestive tract. Thus, among 1148 cases of cancer of the alimentary tract recorded in the Prussian hospitals in 1895 and 1896, 1022, or 89 per cent., affected the large intestine, including the rectum and cæcum.[83] The small intestine is the only part of the digestive tract that is indispensable, and it is attacked to a much smaller extent, providing only 11 per cent. of the cases of intestinal cancer. The probable explanation of these facts is that the contents of the gut remain in the small intestine a shorter time than in the large. Stagnation is a familiar cause of disease, and is the probable cause of the frequency of cancer of the stomach. Of 10,537 cases of cancer of all parts of the digestive tract recorded in the Prussian hospitals in the same period, 4288, or more than 40 per cent., affected the stomach. The latter organ is one that the human body would do well to be rid of. It is not so useless as the large intestine, since it is the chief seat of digestion of albuminous substances, but the small intestine could take its place. Moreover, cases are known in which surgeons have removed cancerous stomachs. The results of such operations were favourable, to the extent that the patients survived and were able to absorb sufficient nourishment. They had to eat rather more frequently, and performed the processes of digestion by means of the secretions of the small intestine and pancreas. It is not surprising to find so many instances of useless or harmful organs in the alimentary tract. Our ancestors were creatures that fed on crude and rough materials, such as wild plants and unprepared flesh. Man has learned to cultivate plants that are digested easily, and to prepare his meats in such a fashion as to be readily digested. The organs that were adapted to the mode of life of the animal predecessors of man have become to a large extent superfluous. Many creatures that have found the opportunity of obtaining their nutriment in a highly digestible condition have lost, more or less completely, the digestive organs. Many parasites are instances of this, as for example the tape-worms, which live in the human digestive tract, bathed by a nutritive fluid which they absorb directly; they have lost the digestive tract completely. In the case of man such an evolution has not occurred, and there remains in the body a harmful organ like the large intestine. In consequence, it is impossible for him to take his nutriment in the most perfect form. If he were only to eat substances that could be almost completely absorbed, the large intestine would be unable to empty itself, and serious complications would be produced. A satisfactory system of diet has to make allowance for this, and in consequence of the structure of the alimentary canal, has to include in the food bulky and indigestible materials such as vegetables.