by holding back the balance-wheel with a needle, and yet not “kill” the watch—for it will resume its movement as soon as the needle is removed—so the changes of the chemical molecules of protoplasm can be arrested, but if the chemical “structure” is uninjured the mechanism of protoplasm can resume its activity when the arresting causes are removed. The inactive, unchanging protoplasm is not “dead,” it has not been “killed” so long as its mechanism is intact. On the other hand, it is the fact that this mechanism—the chemical structure of protoplasm—is very easily destroyed. A unicellular organism is chemically destroyed by crushing or disruption, and the consequent admixture of an excess of water with its particles, also by a temperature high enough to cause pain if applied to our skin, but yet much below that of boiling water, also by strong sun-light, and by very many varieties of chemical substances, especially acids, even when very much diluted. Complex animals and plants are liable to have the protoplasm of essential and important cells of the body destroyed, whereupon the destruction or death of the other cells, not involved in the original trouble, frequently and as a rule results. The protoplasm of the cells of a complex animal is dependent on the proper activity of many other cells besides those of its own tissue or locality in the body. If the protoplasm of certain nerve-cells or of blood-cells or of digestive-cells is poisoned or injured or chemically upset, other cells lose as a consequence—not at once but after a short interval—their necessary chemical food, their oxygen, their accustomed temperature, and so bit by bit the great “body”—the complex organism—ceases to live, that is to say, its protoplasm undergoes step by step and bit by bit irrevocable chemical change or breaking down.