There is no more interesting subject for scientific investigation than the structure and operation, the anatomy and physiology of the human body. That it is an amazingly complex and delicate mechanism, performing a multitude of functions in a wonderfully perfect manner, is, of course, an old story. That in the assimilation of its nourishment and in the growth and repair of its tissue the body obeys the laws of chemistry has long been understood. But that the body obeys in everything the fundamental law of physics, namely, the law of the conservation of energy, has not been so generally recognized. For some years the writer was engaged in some investigations upon this subject.[B] The development of the complex apparatus and unique methods of the research required years of patient labor and study. One of the features of the apparatus was an air-tight chamber, in which a man, as the subject of the experiment, could be confined for any desired period, eating, sleeping, working and living while under minute observation. The experiments usually continued four or five days, but were sometimes prolonged to eight or ten days, and the observations were made and recorded day and night continuously for the entire period. [B] The work was done at Wesleyan University, in collaboration with Prof. W. O. Atwater, under the patronage of the University and the U. S. Department of Agriculture. The atmosphere within the chamber was maintained sufficiently pure to make a prolonged sojourn within its walls entirely comfortable. A current of fresh air, displacing as it entered an equal quantity of air which contained the products of respiration, was maintained continuously. The respired air was analyzed and measured, and the products of respiration from lungs and skin accurately determined. The ventilating air current was maintained by a pair of measuring air pumps, driven by an electric motor. The air was dried, both before entering and after leaving the chamber by freezing out its moisture. This was done by passing it through a refrigerator where its temperature was reduced far below the freezing point. The refrigerator was operated by an ammonia machine, driven by an electric motor. The quantity of air was automatically recorded by the pumps.