Life is an essence that tumbles and pours from its source in creative action and brings into being an infinite variety of forms and kinds of existence. It is the source of the sublime and magnificent, the lovely and beautiful, and the well-spring of enjoyment--in brief, all that is pleasing and delightful in animal and vegetable existence. It is known to us only through its functions and its structures.

D. A. Gorton, M.D., thought that all thought spent in investigating the nature of life is more or less futile, but that "we can, however, with profit, study its phenomena, and thereby deduce its laws and modes of development in animate forms, and its relation to the inorganic world." She was certain that life has a dependent relation to the material world, that "the highest forms of existence are developed and supported by the lower." She adds, "if there is one solitary exception to this remark (that "all are but parts of one stupendous whole"), the great chain of mutual dependence is broken, and there is no certainty of anything."

A fact remains a fact, however we "explain" it. Nothing is removed from the wonderful peculiarity of vital phenomena, by whatever hypothesis we seek to explain them. Whatever is true of these phenomena remains true under any hypothesis. We may observe the phenomena, discover the laws which regulate them, gain an understanding of the conditions that should surround them and learn their limitations and their relations, without knowing what life is. It is not essential to our understanding of the needs of life that we understand its essence.

In the forms of vegetables and animals, organic life is universally diffused upon the surface of the earth. Through the processes of nutrition, circulation, secretion, assimilation, as well as excretion, the power of growth and reproduction gives rise to possibilities of action, since it supplies the instruments of action. It produces bones, muscles, glands, nerves and brain. The growth and reproduction of parts supplies the organic substratum that renders possible all the functions and activities of life. The dynamic capabilities of the human system, as these vary with the conditions and circumstances of life, are built into it during its embryonic period in the forms of organs and structures which provide for a wide variety of activities.

The principle that "organization and function are one," that there is not in the body an independent spirit or principle apart from that inherent in organization may and may not be true; but it is one by which many important facts are explainable. The popular exclusions of this principle from Hygiene and ethics and the practice of addressing every reformatory effort to an abstract ethereal entity, either in or above our organism, is a chief influence in creating the common confusion. In order that we may study the peculiar phenomena of living structures, it does not become necessary that we first solve the questions of the nature and origin of life. We may study the peculiar properties of the living organism without knowing the origin of these properties. The concept, that form is function, is a very useful one. Life is subject to fixed principles and invariable laws; its variety of products and expressions of energy result from the special structural adaptations of which it is constituted and do not rest upon any changes in the laws and principles that govern its operations.

Although anatomical structures are so connected with physiological functions that a correct mode of observation of these functions presupposes an exact knowledge of structure, the physiologist soon comes to realize that the connection between the structure of an organ and its function is often not such that he can directly determine the one from the other. Although it is true that every variety of physiological action is necessarily connected with the special arrangements of the anatomical elements, yet the connection of the two is usually of such a character that it is far from being understood, even after it has been investigated to the minutest details of its structure. It is not difficult to study the structure of a leg or a wing and determine from this what function it is designed to subserve, but it would not be possible from a study of the structure of most organs of the body to determine their function.

We note in such studies that where two organs, such as the eyes, the ears, the kidneys, the hands, the lower extremities, etc., perform identical functions, they possess identical structures and where they serve similar functions, they possess similar structures. As an example of this latter, the great similarity between the salivary glands and the pancreas is such as to lead to the thought that they may serve identical functions. The glands of the body are the most marvelous of fabrics; the body, the most stupendous of factories. Often the slight differences between the structure of one gland and that of another do not seem adequate to explain the differences in their secretions. So alike are the salivary glands and the pancreas that the Germans used to call the pancreas the "abdominal salivary gland." But, while they are both glands and they both secrete digestive juices and enzymes, their secretions are somewhat different and their structures are not identical. In the pancreas are structures that secrete insulin and these differ from the general structure of the pancreas.

Occult to the microscope and unknown to anatomy, but assured by our actions and the necessities of function-structure correlations, the different functions of the different nerve structures require differences in structure. Nerves that feel pain and those that feel heat or cold must be differently constituted, else would all feeling be the same. Perhaps the differences are greater in the centers of nerve activity than in the transmitting fibers, but there are probably differences in the fibers also.

Vital powers and vital properties are synonymous terms. What is "organic power?" We can only answer that it is the capacity or endowment of each organic structure to appropriate suitable materials and resist and reject everything deleterious to its existence and by which it is enabled to use the means adapted to perpetuate its existence and develop to its fullness. It is the power by which we live, move and have our being.

The living organism may be correctly viewed as a hierarchial structure built upon certain basic elements that stand under and support the the rest. It is impossible to really understand a structure apart from its role in the whole organism. An organ is not an independent isonomy, but attains its full significance only in function and when the performance of this function is integrated in the life of the organism, not only of the moment, but for its future. The organs of the body are inseparable parts of an interrelated, interfunctioning and all-including totality.

Without the concept of function, it is impossible to acquire a complete understanding of an organism. No detailed analysis of lifeless fragments derived from living organisms can give us any conception of life. The true significance and value of the particulars of form and structure become apparent only when this knowledge is merged with the infinitely more important study of the vital activity of the different parts. In an organism, whether quite simple or highly complex, the parts are integers of the whole and are necessary for the welfare of the whole--hence the need to maintain organic integrity.

The organs of the living body function by dint of a wisdom incarnated in their very tissues. The total organism functions by dint of this same incarnate wisdom. The human body is not a mere aggregation of assembled parts such as an automobile, but is an intricate and infinitely integrated organization that functions under a central guiding principle that does not seem to be identical with the intellectual powers of man. With their several powers and numerous adaptations, these parts constitute the essential man. The actions that result from this integration and coordination of structure constitute function. Every functional action is the result of the activity of the organ performing it (result of its cause), which is traceable to some ultimate physiological requirement and is correlated with some external relation or condition.

Man is a very complex being; hence, he is not only capable of a higher standard of health than the animals below him in the scale of being, but he is also capable of a wider variety of forms of ill health. Health and available capacities are derived from the harmony of his various parts. The parts of the more complex organisms, being fitted to their positions and functions in the whole, are not interchangeable, as they are seen to be in some of the lower and quite simple organisms.

The powers and expressions of life are limited by the organic substratum and any undue wear and tear of this substratum weakens the capacity of the organism to function, weakens in man both the capacity of sensation and of thought, as well as the powers of vegetative functions, reducing, indeed, all of the organic capacities. It would be unjust to require of man or of an organ more than his or its present organization and surrounding circumstances will permit him or it to perform. It is the part of wisdom to learn to live to avoid any unrecompensable wear and tear upon the vital machinery.

"Soundness of mind," said Trall, "bears an exceedingly close relation to the integrity of the bodily functions." If we can but grasp the uniform and constant connection of mind and body, it will not be difficult for us to understand that the noblest mind requires a home of the most majestic and beautiful form.

Living organisms grow, reproduce and multiply their parts and extend themselves by this repetition. To do this, they select from matter in contact such elements as they have the capacity to arrange as parts of their own structure and they promptly reject and refuse all others, a necessary condition to the maintenance of their vital integrity. In the plant or animal, from the simplest microbe to the largest and most complex organism, or wherever life reigns, assimilation and growth and refusal and rejection are its constant actions and the energy of these acts must bear a constant relation to each other, for the vital endowment equally seeks its own welfare in either act.

As the constitution of the vital molecule is uniform and invariable, it follows that all external matter must be of three kinds: one is identical with it, or is susceptible of being transformed into the same form and exercising the same relations and may be called aliment; the second is indifferent, giving rise to no change in contact, but may serve as a divisor, as water; or, a third, such as gives rise to relations that would be antagonistic and destructive to the integrity of the vital molecule in various degrees of intensity. Consequently, this last class must be composed of very many subdivisions--indeed, almost as various as the number of chemical elements and compounds, after subtracting the aliments. This last class must be denominated poisonous. It is necessary to life that the living organism shall resist and expel all substances that it cannot transform into materials identical with its own substance. It is these processes of resistance and expulsion and the processes by which damages are repaired that are mistaken for the actions of drugs.

The animal body is composed of many parts and these parts of lesser elements, each of which is possessed of a certain quasi-independence of action peculiar to itself and so is capable of being affected in a peculiar manner; hence, the application of foreign matter to the general organism through the circulation produces local effects, all of which are alterations of the normal functions and structures and tend to degrade, not to elevate these.

All of this is the result of the invariableness that characterizes the constitution of all things. The same elements and the same conditions of heat, etc., are employed in the constitution of each individual and each species, wherever produced; the same law is ruling throughout the realm of life. The attempt to impose other materials or conditions upon organic structure is resisted and can only result in waste of the formative and actuating principles employed in its constitution. A constant development of forms, of which the vital organism is connected and on which it depends, is thus retarded or prevented.

Throughout the chapters of this book we have used the phrases vital organism and vital activities. It is necessary that we explain the meaning with which we use them. The term vital is derived from the Latin word for life and we use it in this book in this sense. By vital organism we simply mean the living organism and by vital activities we have no other meaning than the activities of the living organism. We do not use the term vital with reference to any theory of the nature and source of life.