The real argument lies deeper; it lies in the relation of these minerals (inorganic matters) to the living system. If they are usable, they are useful; if not, they are injurious. Physiology reveals to us that, except for water and oxygen, no inorganic matter of any kind can be used by the animal organism. It must derive its nutritive materials from the vegetable kingdom.
Not all organic materials are usable as food. Such vegetable alkaloids as morphine (from opium), caffeine (from coffee), theine (from tea), nicotine (from tobacco), although they will get into the blood stream, cannot be metabolized by the organism. Organic materials are foods only if they can be reduced, by the process of digestion, to certain simple and assimilable products. Even protein, as essential to life as this is, is a virulent poison if introduced directly into the blood stream without first undergoing digestion. The intravenous introduction of amino acids into the body in an effort to feed the sick organism that cannot take food is followed by symptoms of anaphylaxis, damages to the kidneys and a progressive loss of weight. They do not seem to be metabolizable.
Because of different capacities to utilize organic materials possessed by different animals, organic substances that are poisonous to one animal may prove to be wholesome food to another. An example is belladonna, which contains two toxic substances, neither of which can be broken down by man. The rabbit possesses enzymes that digest the toxins of belladonna; hence, while belladonna is a rank poison to man, it is a wholesome food to the rabbit. Rabbits do not secrete the enzyme that breaks down the toxins of belladonna before they are six weeks old; hence, belladonna is poisonous to rabbits before this age.
Man's mental and physical efficiency depends very largely upon his ability to select and assimilate food. Without this ability, all those changes within the body involved in the synthesis of structure and the performance of function could not take place. All phases of vital activity depend on material conditions; and so long as man remains man, this will remain true. An example of this is provided us by the failure of the effort to introduce oxygen directly into the blood. In the early part of this century a method was devised of introducing oxygen directly into the blood as a means of curing disease. It proved to be as abortive as have all other efforts designed to flout the normal order. Oxygen by injection was no more useful than salts or sugars or amino acids by injection. The process of extracting oxygen from the air, by the lungs, is unquestionably one that is subject to as well defined laws as the assimilation of solid matter and all efforts to flout these laws must end in failure.
Nature is replete with an abundant variety of wholesome, delicious foods, the constituent elements of which are exactly adapted to the structures and functions of our organism. With this self-evident fact before their eyes, the proof of which is spread out as broad as the pages of nature, men continue to try to improve the human dietary by fragmentizing and refining nature's products. Even our health food stores sell wheat bran, rice polishings, vegetable margarines, vegetable oils, powdered skim milk, gluten bread, vitamin extracts and other food fragments. Our food processors are continually worrying their brains and working their laboratories in an endeavor to get something into the human stomach that nature does not produce. They are trying to improve the healthfulness of our foods by separating them into fragments or by changing them so that they are unrecognizable.
The kind of food eaten by each animal species in its natural state is determined by its structure and it is led by instinct to eat those foods for which its structure fits it. Carnivorous animals have a short and very simple digestive tract, while those of the herbivorous and graminivorous animals are very complex, some of them even having three or four stomachs. Carnivorous animals are also commonly supplied with talons and claws and with teeth designed to catch and rend their prey. These indications must be observed with discrimination, as faulty observations have led to error. For example, a marked development of the canine teeth, standing alone (as among the anthropoid apes), does not indicate a carnivorous nature. Different species employ their canine teeth for different purposes.
Discussing this very subject Trall says: "A reference to the anatomical structure of the digestive system shows a very complex structural arrangement and this implies a correspondingly elaborate process in the manufacture of food into blood, and thence into the various structures of the body.
"Many animals, as the carnivores, have a simpler digestive structure, and are adapted to subsist on food requiring less change and elaboration; but it seems to be a law of the whole animal kingdom, that the finest, most important, most highly-vitalized and most enduring tissues are formed of food which requires a slow and, hence, admits of a more perfect elaboration.
"For this reason alone, vegetable food affords a better, a lighter, a more perfect nutriment than animal food, which is nothing more or less than degenerated vegetable material."
While every animal organism possesses the capacity to make use of several different kinds of organic materials from different sources, each form of life thrives and develops best on those foods to which the peculiarities of its digestive system is specially adapted. The more perfect and complete the adaptation of food to digestive apparatus and enzymes, the more striking and perfect will be the structures and functions of life. The food to which one animal is peculiarly adapted can never be made to subserve the purposes of another and differently organized animal in the same satisfactory manner. Each type of animal life is possessed of organization that is adapted to its appropriate food and such food is best fitted to subserve its physiological needs. Scientists do not dispute about the natural or proper food for any of the lower animals; but when they come to a consideration of man's normal diet, there is the greatest diversity of opinion.
The food-gathering instincts of animals are correlated with the structures and functions of these animals. Can we doubt that, in his prime, before he had acquired a conditioning culture and before necessity had caused him to deviate from his biological and physiological norms, the same correlation of food habits and structural adaptations guided man in his food gathering? Is man not subject to the "law of specific adaptation?" Is he the only animal in all nature devoid of guiding instincts?
It is pure sophistry to argue that because a practice of eating or of drinking or the eating of any article of food is in general use among men, it is, therefore, right and best for man. This is a common fallacy that most works on dietetics seek to maintain. The same fallacy is frequently employed to support such drug habits as the tobacco, alcohol, coffee, opium, arsenic, betel, etc., habits. Because the use of these poisons is so nearly universal, it is argued that they must meet some real want in the human system.