=Chemical activity= is a property of protoplasm. In its network combinations and decompositions are effected more extensive in range than any which a chemist can cause to occur in his laboratory. From ammonia, carbonic acid, and water, a plant makes albumin. A chemist cannot make albumin, no matter how complex may be the nitrogenous substances which he endeavours to cause to combine. Albumin is resolved by animals into water, carbonic acid, and urea. Cells of the gastric glands set a problem which puzzles the chemist by making hydrochloric acid from sodic chloride without the intervention of a “stronger” acid. Many other illustrations of the same kind might be cited. Although the tissues of animals act chiefly as destroying agents, their protoplasm is not without constructive power. There is apparently no limit to the capacity for synthesis of plants. The chemistry of living things may be divided into two provinces, absolutely antagonistic in the series of reactions which they comprise. The one series is constructive, synthetic; the other destructive, analytical. Construction involves the locking up of energy. It is endothermal. Destruction results in the setting free of energy. It is exothermal. To accomplish synthesis energy must be added. Plants obtain it from the sun’s rays. Animals disperse energy, set free by the analysis of substances formed in plants, in maintaining their bodies’ warmth and movement. The chemistry of the laboratory and the chemistry of protoplasm present certain contrasting features. A chemist reaches the compound which he wishes to form by effecting a series of interchanges. For example, he wishes to form uric acid by uniting a nucleus contained in lactic acid with urea. First he introduces chlorine and ammonia into the molecule of lactic acid. He makes trichlorlactamide. Then he heats (supplies energy to) a mixture of trichlorlactamide and urea. Two of the chlorine atoms carry off hydrogen atoms from the urea. A third leaves the trichlorlactamide with its ammonia. Water also breaks away. Uric acid remains. Trichlorlactamide Urea Uric Acid CCl₃CH.OH.CO.NH₂ + 2(NH₂)₂CO = C₅H₄N₄O₃ + NH₄Cl + 2HCl + H₂O.