While excessive work, even with a liberal dietary, produces more waste in the system than can be compensated by the food which is taken, it is equally true that rest with a liberal dietary would be more injurious than excessive labour, and the typical system with regard to the proportion of food to the amount of work would be one which exactly supplied the amount of nutritive material accurately adjusted to the waste going on in the system. There are no means, however, of calculating this with absolute precision, and the matter is, therefore, necessarily left to experience.