Bacteria are minute vegetable organisms, which exist in the dust of the air, in water and almost everywhere on or near the surface of the earth. They are consequently taken in with our food. They exist in the mouth; those in carious teeth are often sufficient to injuriously affect digestion and health. The healthy gastric juice is to a great degree antiseptic, but few bacteria being able to endure its acidity. When the residue of the food reaches the large intestine, bacteria are found in very great numbers. The warmth of the body is highly favourable to their growth. They cause the food and intestinal _debris_ to assume its fæcal character. Should the mass be retained, the bacterial poisons accumutate and being absorbed into the body produce headaches, exhaustion, neurasthenia and other complaints. Proteid matter, the products of its decomposition and nitrogenous matter generally, are especially the food of bacteria; this is shown in the offensiveness of the fæces of the carnivora, notwithstanding their short intestines, compared with that of the herbivora. Also in the difference of the fæces of the dog when fed on flesh and on a nearly vegetable diet. On a rich proteid diet, especially if it consists largely of flesh, the bacterial products in the intestines are greater than on a vegetable diet. On the latter such a disease as appendicitis is rare. Professor Elie Metchnikoff, of the Pasteur Institute, thinks that man's voluminous and highly developed large intestine fulfils no useful purpose, and on account of its breeding a very copious and varied bacterial flora, could with advantage be dispensed with. He also has said that man, who could support himself on food easily digestible, has a small intestine which is disproportionately fully developed. Instead of having between 18 and 21 feet of small intestine, man might do with one-third of that length. According to him, there is a disharmony of our food and our digestive system. Referring to such views, and the desire of some surgeons to remove the vermiform appendix and portions of the intestines upon too little provocation, Sir W. Macewin, M.D., F.R.S. (_B. Medical Jrn._, 1904, 2 p. 874) says:--"Is this human body of ours so badly constructed that it contains so many useless parts and requires so much tinkering? Possibly I may be out of fashion with the times, as I cannot find such imperfections in the normal human body as are alleged. On the contrary, the more one looks into the human body and sees it work, the better one understands it and the more one is struck with the wondrous utility, beauty, and harmony of all its parts." Our food we can change, but not our organs-except by a dangerous surgical operations. Our teeth with our complex and very long intestines are adapted for fibrous, bulky and solid food. On such food mankind has lived for an immense period of time. It is true that there are several theoretical advantages in