This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
If we go beyond the tissues to seek the ultimate constituents of the body, we must lay aside the microscope, and call in chemistry to our aid, to discover what elements and compounds make up the cells and intercellular substance.
How does the division of duties in it affect the human body? What is the object of the distributing mechanism? What of the regulating? What are the distributing organs in the body called? What is the object of the nerve organs?
Of the many elements discovered by chemists, only sixteen have been found in the healthy human body.* Very few exist in it uncombined. Some oxygen is dissolved in the blood; and that gas is also found, mixed with nitrogen, in the lungs.
These are so numerous that it would be a long task to enumerate them, but some require mention: they may be divided into organic and inorganic. In a general way we may say that the organic constituents of the body, if all water were separated from them, would burn if put in a fire; and the inorganic components could not be made to burn.
Of the inorganic constituents of the body, water and common salt are the most important; they are found in all the organs and liquids of the body. Phosphate and carbonate of lime are found in large proportions in the bones and teeth; and free hydrochloric acid (spirits of salts or muriatic acid) may always be found in healthy gastric juice, which dissolves some kinds of food in the stomach.
All organic constituents of the body contain carbon, hydrogen, and oxygen; some contain nitrogen also. There are three chief kinds of them, viz.: albumens, fats, and carbohydrates.
How many chemical elements exist in the body ? Are most of them free or combined with others? Name those found free.
Into what main groups may be divided the chemical compounds existing in the body? Name some of the chief inorganic compounds helping to build the body. Where are they found in it ?
What do all organic substances in the body contain ?
* The elements found in the body in health areŚcarbon, hydrogen, nitrogen, oxygen, sulphur, phosphorus, chlorine, fluorine, silicon, sodium, potassium, lithium, calcium, magnesium, iron, and manganese.