the cell is the unit of structure in the form of which protoplasm invariably appears.5 We must not think of protoplasm as a fixed compound: there are different protoplasms. Plants are composed largely of oxygen, hydrogen, and carbon. The human body contains: carbon 13.5 per cent, hydrogen 9.1 per cent, oxygen 72 per cent, nitrogen 2.5 per cent, calcium 1.3 per cent, phosphorus 1.15 per cent, sodium or. per cent, iron 0.01 per cent, magnesium 0.001 per cent, and traces of silicon and fluorine. Although the structural materials are similar the results are very different. That which should be emphasized here is that organisms are made up of cells which consist of matter arranged in certain ways and that the phrase "vital principle" is but the term applied to the behavior of matter so arranged. Temperature of Organisms Now that we have had a glimpse of the structure of organisms let us consider some of the conditions under which they function. It has been suggested that organic compounds are sensitive and subject to change. These changes are largely chemical in nature and such changes depend much on temperature. The maintenance of a fairly stable temperature would seem, then, to be necessary. It cannot be an accident that the various types of life have characteristic temperatures at which they prosper. Some bacteria will live and multiply in water at a temperature of 32° while other sorts flourish in hot springs where the thermometer registers 170°. The human body has a normal temperature of 98.5°, being lower at night and lowest in the early morning. If attacked by fever the temperature rises, and if it reaches 105° we know that the patient is in a dangerous condition and the same is true if the temperature falls to 93°. Changes in bodily temperature probably produce new chemical compounds. We perish from cold long before the body is actually frozen. Physical exercise raises the temperature about one degree and we begin to perspire. This reduces the amount of water in our bodies and we get thirsty. We find it harder to keep cool than to keep warm for if we are cool we put on clothes or exercise and go about our business. Our clothing is a better conductor of heat than is the air but is valuable because it keeps a layer of air about the body. In order to keep our bodily temperature fairly even we burn (oxidize) a large part of the fats and carbohydrates that we eat. By weight, some 68 per cent of the body is water. An adult weighing 168 pounds produces while at rest some 2,400 calories (heat units) daily, or sufficient to raise the body temperature 57°. Since this does not take place he must lose about 1.5 calories per kilo per hour. If we could substitute most other substances that we know for the water, the heat produced would raise the temperature from 180° to 270°. Thus in our bodies, as well as in our houses, we find that water gives the most even temperature. Properties of Water Of all known substances water is the best fitted for the service just mentioned and it is the only one existing in adequate quantity. Its specific heat is very high, being exceeded only by hydrogen and ammonia, and if atomic weight be considered also, it stands at the top of the list. The freezing point of water is about 100° higher than that of most substances. This means that the latent heat of water is very high, being surpassed by ammonia only. Since water expands when it changes to ice, the actual freezing of more than the surface of a body of water is practically impossible. Water evaporates readily. At the equator some 62 feet of water are taken yearly from the This spreads over the earth and surface of the ocean. prevents the rapid dissipation of the heat received from the sun during the day, not only modifying the temperature of the different zones but bringing rain to regions otherwise arid. Ammonia might rival it in these regards but ammonia is nowhere common and it has other qualities which are less desirable. Water is a splendid solvent and thus makes possible many of the combinations needed by organisms. Its surface tension (75) is exceeded only by that of mercury (436) and as a result its capillary action enables it to penetrate the recesses of the earth as indicated in the preceding chapter and to find its way into the cells of plants and animals. Taking all of these things into consideration it is evident that life as we know it is absolutely dependent on water. Carbon and Its Compounds Wherever there is life there is carbon, and organic chemistry might be called the science of carbon compounds. Of these over a hundred thousand are known. Many of them are simple, like carbonic acid; others are so complex that a line would be required to write the formula. This element is peculiar in that it has the power of uniting with itself, as well as with other substances, and thus is able to build up the large molecules containing a great number of atoms which characterize living structures. Moreover, such carbon molecules are relatively stable and thus give a needed permanency to delicate organic substances. "It is a curious fact in nature that there seems to be a position of great stability when groups of six carbon atoms unite in little galaxies or concatenations. Although such groups of less, or occasionally more, than six carbon atoms are formed naturally by life processes, by far the greater portion of the substance of living organisms is built up of six carbon groups and multiples of them." ... Carbonic acid enters and leaves water freely and is always associated with it. From the first "it has steadily fulfilled the function of regulating the reaction of protoplasm and of body tissue and fluids. The one chemical process which is open if any transformations whatsoever are to be accomplished with carbonic acid and water leads directly and to all appearances to the greatest complexity that has been found in any one chemical process; to a system made up of possibly two hundred substances or more, most of which possess very great chemical activity." " Carbon forms an important part of most of our foodstuffs. In the sugars and starches (carbohydrates) there are thirty or forty of these great carbon groups joined together. The fats are formed by the substitution of hydrogen for part of the oxygen contained in the carbohydrates while in the proteins we find nitrogen and, sometimes, phosphorus, sulphur and iron. Let us see what happens in the human body. Haldane found that the respiratory sacs of the lungs always contained 5.5 volumes of carbon dioxide to every one hundred volumes of air. ... He observed that if the proportion of CO2 becomes higher then the breathing is quickened, thus washing out more CO2 from the respiratory chambers and replacing it with air. If the proportion becomes less than normal, then the breathing is slowed until the usual proportion is restored. Not only are the respiratory nerve centers disturbed by an excess of CO2 in the blood supplied to them; they are also thrown into an equally excitable state if there should be a deficiency of oxygen. The rate of our breathing is automatically controlled by the percentage of oxygen and carbon dioxide in the arterial blood-the two substances connected with combustion.8 Oxygen enters the scene with its "unparalleled instability." "The body at rest requires this constant supply of oxygen-250 c.c. per minute-to supply the heart (its muscular blood-pump), the muscles of respiration (which work its air-pump), and other muscular engines, such as stomach and bowels, with the means of burning and restoring the lactic acid which each of them is continually forming.” 9 The blood gets its oxygen in the lungs. This is carried through the body to do its regenerative work and the carbon is carried back to be thrown out through the lungs. In violent exercise the oxygen supply must be greatly increased. ORGANISMS as CHEMICAL ENGINES An organism, then, is a chemical engine made up of a multitude of parts, each having its own function and the welfare of the whole depending on the coördinated functioning of each part. The food must be transformed by that process which we call digestion into bone and muscle or burned to produce heat. Limiting our illustrations to the human body, we know that nature has achieved a wonderful correlation. Gradually man has come to understand how the body works though many things still puzzle him. Our everyday language still carries hints of long-discarded interpretations as, for instance, when we say that a man has melancholia (black bile) or that he is hard-hearted. Only yesterday we learned the importance of the ductless glands hitherto considered of little importance. The suprarenals, two glands not over an ounce in weight, secrete adrenalin which stimulates the arteries in times of emergency and stimulates the liver to release its supply of fuel (sugar) into the blood. The thyroid gland makes the tissues sensitive and "greedy for oxygen," while their failure produces the cretin. The little pituitary gland at the base of the brain controls body growth and, if overdeveloped, causes giantism. The sex glands are responsible for the traits peculiar to each sex. If the body is to maintain an upright position there must be a bony framework strong enough to support the weight and yet to be flexible. Fortunately nature has discovered in lime a material that will work and remain substantially permanent. Through |