In this example the trichlorlactamide may be said to exchange its chlorine and ammonia for urea. When he planned the reaction, the chemist foresaw what would happen. He knew that if he weakened the grip of the lact radicle upon them, chlorine and hydrogen, chlorine and ammonia, oxygen and hydrogen, would take the opportunity of getting away together. The lact radicle and urea would be left with dangling arms, which must “satisfy their affinities” by linking up. It would be rash to assert that any reaction is impossible to Nature’s chemistry; but it may safely be said that the reactions which protoplasm effects are, so far as we know them, of a different type from this laboratory example. Uric acid is the chief excrement of birds. It is made in the liver. If the liver is shut off from the circulation, lactate of ammonia is excreted in the place of uric acid. It is therefore, in all probability, lactate of ammonia which the liver transforms into uric acid. We cannot pretend to say how this is done, although an empirical formula for the change might be drafted easily enough. Lactate of ammonia has the formula NH₄C₃H₅O₃. Uric acid, C₅H₄N₄O₃, contains a much higher percentage of nitrogen. It could be produced from lactate of ammonia by the condensation of the nitrogen-containing nucleus and the addition of a sufficient amount of oxygen to complete the oxidation of the superfluous carbon and hydrogen into carbonic acid and water. It is of little interest to count the number of atoms concerned in this process. If a bird be fed upon urea, or even upon various salts of ammonia, its liver will change them into uric acid. Lactate of ammonia is the nitrogen-containing compound with which the liver has normally to deal. It can handle almost any other combination of nitrogen with equal ease. In the protoplasm of the liver the atoms in the molecule of lactate of ammonia are rearranged. The molecules are condensed; water is set free; oxidation occurs. It seems almost as if molecules, when in contact with protoplasm, lose their individuality. Their atoms fall into new groups. Chains which the chemist finds so difficult to break—chains from which he can remove a link only by insinuating another and a stronger—are, when in contact with protoplasm, groups of isolated links. The links rearrange themselves. They join into new circlets, larger, smaller, more open, closer. As grains of sand on a metal plate group themselves in harmony with the vibrations caused in the plate by drawing a violin bow across it, so the atoms answer to the forces which set protoplasm vibrating. There is no waste of force. The chemist may need to enclose sawdust and lime in a crucible heated in an electric furnace if he wishes to compel them to combine as carbide. He supplies energy enormously in excess of the amount which the new compound will lock up. Under the influence of protoplasm the reactions which occur are exactly proportional to the amount of energy supplied.