[11] Currie, _Med. Rep._, vol. i., p. 163. Here then we have obtained an important amendment of our notion of a narcotic. A narcotic is a substance which, taken in the requisite dose, causes paralysis. But we have seen that by diminishing the dose we at last reach a point where the narcotic entirely ceases to act as a narcotic and becomes a stimulant. What then is a stimulant? There is a prejudice afloat which interferes with the proper apprehension of this word. People call alcohol, indiscriminately, a stimulant; and when a man gets drunk, he is incorrectly said to be stimulating himself; stimulants are therefore looked at askance, as things which demoralize. The reader is already in a position to know better than this. He sees already that it is not stimulus but narcosis which is ruining the drunkard. Nevertheless, that he may understand thoroughly what a stimulant is, we must give further explanation and illustration. Food and stimulus are the two great, equally essential factors or co-efficients in the process of nutrition. We mean by this, that in order to nourish your system and make good its daily waste, you need both food and stimulus. You must have both, or you cannot support life. Day by day, in every act of life, be it in the acts of working and thinking which go on consciously, or be it in the acts of digestion and respiration which go on unconsciously, in the mere keeping ourselves alive, we are continually using up and rendering worthless the materials of which our bodies are composed. We use up tissue as an engine uses up fuel; and we therefore need constant coaling. Tissue once used is no better than ashes; it must be excreted, and food must be taken to form new tissue. Now the wonderful process by which digested food is taken up from the blood by the tissues--each tissue taking just what will serve it and no more, muscle-making stuff to muscle, bone-making stuff to bone, nerve-making stuff to nerve--is called assimilation, nutrition, or repair. It is according as waste or repair predominates that we are feeble or strong, useless or efficient. When repair is greatly in excess, as it usually is in childhood and youth, we grow. When waste is greatly in excess, we die of consumption, gangrene, or starvation. When the daily repair slightly outweighs the daily waste, we are healthy and vigorous. When the daily repair is not quite enough to replace the daily waste, we are feeble, easily wearied, and liable to be assailed by some illness.