Experiment 80. _To show that bile favors filtration and the absorption of fats_. Place two small funnels of exactly the same size in a filter stand, and under each a beaker. Into each funnel put a filter paper; moisten the one with water (_A_) and the other with bile (_B_). Pour into each an equal volume of almond oil; cover with a slip of glass to prevent evaporation. Set aside for twelve hours, and note that the oil passes through _B_, but scarcely any through _A_. The oil filters much more readily through the one moistened with bile, than through the one moistened with water. Experiments with the Fats. Experiment 81. Use olive oil or lard. Show by experiment that they are soluble in ether, chloroform and hot water, but insoluble in water alone. Experiment 82. Dissolve a few drops of oil or fat in a teaspoonful of ether. Let a drop of the solution fall on a piece of tissue or rice paper. Note the greasy stain, which does not disappear with the heat. Experiment 83. Pour a little cod-liver oil into a test tube; add a few drops of a dilute solution of sodium carbonate. The whole mass becomes white, making an emulsion. Experiment 84. Shake up olive oil with a solution of albumen in a test tube. Note that an emulsion is formed. Chapter VII. The Blood and Its Circulation. 177. The Circulation. All the tissues of the body are traversed by exceedingly minute tubes called capillaries, which receive the blood from the arteries, and convey it to the veins. These capillaries form a great system of networks, the meshes of which are filled with the elements of the various tissues. That is, the capillaries are closed vessels, and the tissues lie outside of them, as asbestos packing may be used to envelop hot-water pipes. The space between the walls of the capillaries and the cells of the tissues is filled with lymph. As the blood flows along the capillaries, certain parts of the plasma of the blood filter through their walls into the lymph, and certain parts of the lymph filter through the cell walls of the tissues and mingle with the blood current. The lymph thus acts as a medium of exchange, in which a transfer of material takes place between the blood in the capillaries and the lymph around them. A similar exchange of material is constantly going on between the lymph and the tissues themselves. This, then, we must remember,—that in every tissue, so long as the blood flows, and life lasts, this exchange takes place between the blood within the capillaries and the tissues without. The stream of blood _to_ the tissues carries to them the material, including the all-important oxygen, with which they build themselves up and do their work. The stream _from_ the tissues carries into the blood the products of certain chemical changes which have taken place in these tissues. These products may represent simple waste matter to be cast out or material which may be of use to some other tissue.