2. A second portion of energy is required to do the mechanical work of the body. When a locomotive hauls a loaded train up grade, or steams up grade alone, it is doing work in proportion to the total weight and the height to which it is carried. So when a man walks up hill or climbs a ladder he is lifting his body against the force of gravity, and hence doing work. If his weight be 200 pounds he is doing twice as much work as though he weighed only 100 pounds. If a man weighing 150 pounds climbs Bunker Hill Monument (220 feet), 33,000 foot-pounds of work will then be done; and if he succeeds in making the ascent in one minute, he would be doing work at the rate of one full horse power for that minute. If he climbs a mountain two miles high in three hours and twelve minutes he would be doing work in so lifting his body at the rate of one quarter of a horse power. This is, of course, a faster rate of work than an average man could maintain. In all the functions of daily life the body is necessarily doing some mechanical work. Even dressing and eating require a certain expenditure of energy, and in ordinary business and manual labor the amount of mechanical work done is considerable. Moreover, a large amount of work is done by the heart in pumping the blood through the circulatory system, and by the chest in respiration. This, then, the internal and external work done, as in the locomotive, represents the second portion of energy derived from the food eaten. 3. The warm air, carbonic acid gas and water vapor passing away from the lungs in respiration carry with them a large amount of heat. This corresponds to the loss of heat in the locomotive through the smoke passing out the smokestack, and in both cases the loss is greater when work is being done and less during inaction. The refuse products of the body (as the ashes of the locomotive) also carry away heat. This is the third portion of heat and is a large one.