THE HUMAN BODY AS AN ENGINE.
By Professor E. B. ROSA.
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.
The chamber was so constructed and fitted with electrical and other devices as to afford the means of measuring the quantity of heat which the subject of the experiment gave off from his body. And in order to keep the temperature of the room constant this heat was absorbed and carried away by a stream of cold water, the latter flowing through a series of copper pipes within the chamber, and coming out considerably warmer than it entered. So delicate were the regulating devices that the temperature could be maintained constant, hour after hour, to within one or two hundredths of a degree. In some cases the man under investigation worked regularly eight hours a day, the work done being measured by apparatus designed for the purpose.
Food and drink were passed into the chamber three times a day through an air-tight trap. Both were accurately weighed, their temperature recorded and samples reserved for chemical analysis. Solid and liquid excreta were likewise weighed and analyzed. The observations, analyses and computations of a single experiment thus involved a vast amount of labor and expense, which was only justified by the importance of the question under investigation. In order to be able to understand just what this question is, let us see what is meant by the conservation of matter and energy in the physical world.
The impossibility of creating or destroying matter is very generally recognized. Its forms or properties may be altered, chemical and physical changes may be effected, it may, indeed, vanish from sight, but its quantity remains unchanged. Thus ice may turn to water and water to invisible steam, but the total quantity or mass of the substance remains constant; and if by refrigeration the steam be brought to the condition of ice again, there will be precisely the same amount as before. These are physical changes and are easily effected. We simply apply heat to melt the ice and then more heat to vaporize the water. Conversely, withdrawing heat will condense the vapor to water, when a further subtraction of heat will change the water into ice.
Again, wood disappears when burned and seems to be destroyed. And yet we know that the weight of the resulting smoke and ashes is exactly equal to that of the wood. The matter has been changed in form and composition, but its mass cannot be altered. It is not so easy to bring the smoke and ashes into combination again and so restore the matter to its original form as in the case of ice and steam. But this is done by nature. Ashes go to the soil, smoke into the atmosphere. The forces of nature bring these elements together again in plant and tree, and so it comes about that the materials resulting from the burning of wood again become wood, and over and over again the cycle is repeated as time rolls on. Many other examples might be cited to show what is meant by the indestructibility of matter, or the conservation of matter; but these will suffice to show that the one essential fact is that the matter or stuff of a body cannot be destroyed.
Although matter is protean and its transformations limitless, there are certain changes which cannot be made. Iron cannot be turned into silver, nor silver into gold, nor oxygen into nitrogen. There appear to be indeed about seventy or eighty distinct kinds of matter, and so far as we know one cannot be converted into another. They may be united in countless combinations, but each is itself not only indestructible but unchangeable. Why this is so is an interesting subject of speculation. We do not positively know.