The colourless liquid of the blood contains, besides the red corpuscles floating in it, others brought to it in the lymph and derived from various connective-tissue spaces and special nodules or "glands." They are outnumbered by the red corpuscles in the proportion of five hundred to one. They are colourless, and bigger than the red corpuscles. Most of them continually change their shape, and consist of active, moving protoplasm. These are the "phagocytes," which, besides acting chemically upon the constituents of the blood-liquid, take into their substance (as does the amœba or proteus-animalcule) and digest and destroy all foreign or dead particles, and the bacteria which may find their way into it. They pass out, forcing their way through the excessively thin walls of the finest capillaries--blood-vessels not wide enough to admit two of them side by side--and enter, to the number of thousands, the tissues which have been wounded or poisoned by bacteria, to carry on their all-important protective "scavenger" or "police-constable" work. Inflammation is the slowing of the blood-stream by dilatation of the vessels at an injured spot, in order to allow the phagocytes to make their way out of the blood-stream into the tissues, and so get to close quarters with the enemy. There are other excessively minute dustlike particles called "platelets," which are sometimes very abundant in the liquid of the blood. Besides the duties of oxygen-carrying and scavengering the blood has other great and vitally important business. It has to distribute nutriment, to pick up waste oxidized chemical products and get rid of them, and to distribute and equalize the heat which it carries around the body like a perfect hot-water warming installation. CHAPTER XXXV FISH AND FAST DAYS MOST people are familiar with the fact that fasting in the Christian Church has from early times been of two degrees--one in which no flesh of beast or bird or fish, not even eggs, not even milk, may be consumed, and a less severe degree in which the eating of fish is allowed. It is not at first sight clear why the eating of fish--and even of birds such as the Barnacle goose and the Sooty duck, supposed to be produced from fish--has been permitted by the Christian Church, since the flesh of fish is highly nourishing and an excellent substitute for the meat of beasts and birds, and a man fed upon it is far from suffering the effects of true "fasting." Many races and out-of-the-way people live entirely upon vegetables and a little fish, and do very well on that diet.