The New Student's Reference Work/Physiology
Phys′iol′ogy. Anatomy shows us that animals and plants are wonderfully constructed. But after we understand their architecture and even their minute structure, the questions remain: What are all the organs and tissues for, and what takes place within the parts that are actually alive? Physiology attempts to answer questions of this nature. It therefore stands in contrast with anatomy and is supplementary to it. The activities of the body are varied and depend on life for their manifestation — they may be called vital activities. Physiology embraces a study of them all. This subject began to attract the attention of the ancient medical men, who wished to fathom the activities of the body in order to heal it in disease. But it is so difficult a thing to begin to comprehend the activities of life, that even the simpler relationships were imperfectly understood, and they resorted to mystical explanations. They spoke of spirits and humors in the body as causing the various changes. The arteries were supposed to carry air, the veins only blood, and nothing was known of the circulation. In these early days, also, anatomy, physiology and medicine were united into a poorly digested mass of facts and fancies. This state of affairs lasted till the 16th century, and then the awakening came through the efforts of gifted men endued with the spirit of independent investigation. The advances made depended upon the work or leadership of these men, and certain periods of especial importance should be pointed out.
First is the period of Harvey (1578-1657). In his time the old idea of spirits and humors was giving way, but there was much vagueness about the relationships and activities of the body. He helped to illuminate the subject by showing a connection between arteries and veins and demonstrating the circulation of the blood. Harvey (q. v.) did not see the blood passing through the capillaries from arteries to veins, but his reasoning was unassailable that such a connection must exist and that the blood makes a complete circulation. He gave this conclusion in his medical lectures as early as 1619, but did not publish his views until 1628. It was reserved for Malpighi, in 1661, actually to see the circulation through capillaries under the microscope, and for Leeuwenhoek, in 1669 and later years, greatly to extend the observations. The next great period was marked by the work of Haller (1708-77), who made physiology an independent subject. It had previously been united with anatomy and medicine; he made it a subject to be studied for its own sake. The period that marks the beginning of modern physiology came next, and was due to the genius and force of Johannes Müller (q. v.). He studied physiology so broadly that he made it comparative. He used every means at his command — experiment, observations on simpler animals, the microsope, the discoveries in physics, chemistry and psychology. He (1801-58) made physiology systematic and broadly comparative. Not only did he do important work himself, but as professor of physiology at Berlin he trained many talented young men, among whom were Ludwig (1816-95), Du Bois-Raymond (1818-96) and Helmholtz (q. v.). Thus his influence reached to the present time and affected recent physiology. With these distinguished German physiologists should be mentioned Claud Bernard (1813-78) of France and Sir Michael Foster of England (1816-).
Physiology has broadened and deepened until it includes the vital activities of the entire animal and vegetable worlds. Every action or function dependent upon life is embraced by it. These are so varied that they must be reduced to order and system, and, when that has been done, we observe that all the functions may be grouped under three great headings: Those concerned with nutrition; those connected with relation; and those pertaining to reproduction. Nutrition embraces every activity concerned in nourishing the body. It must include a discussion of the blood, its structure, circulation and changes; the heart and the influences which affect it; the digestive system, the kinds of food, the nature of digestion, the absorption of the food into the circulation, the secretion of substances like the digestive juices and other forms of secretions in the body; and the action of the liver, pancreas and similar organs. Respiration is connected with nutrition, because the oxygen brought in is used in all processes of the body, and the removal of the carbon dioxide (CO2) is an aid to nutrition. One must, therefore, learn all about the breathing organs and the nature of the exchanges between the blood, the air and the tissues. The living protoplasm of the body is continually undergoing disintegration; it breaks into carbon dioxide, water and nitrogenous compounds. In order that nutrition may be effectively carried on, these waste-products must be removed. This topic includes the action of the kidneys, the lungs and the skin. The varied chemical changes in assimilating the food and the reverse set of changes resulting in the liberation of energy must be considered under nutrition.
Another great division of physiology deals with the means by which an animal or plant is brought into proper relation with its surroundings. This in higher animals includes the action of the nervous system and sense-organs as well as control of the nervous system over the organs. The muscles and organs of protection are also involved in bringing about a harmonious relation between surroundings and the animal. Finally, reproduction refers to the preservation of the race, and is more for the benefit of the race, generally speaking, than for the individual.
A study of all these varied activities is physiology. Reference must be made to text-books and manuals for further consideration. It is a common fault with our elementary physiologies to go too much into the discussion of the effects of alcohol and narcotics. The importance of such a discussion is unquestioned, but the facts of physiology and hygiene should stand out in unrivaled prominence. Among the smaller texts Huxley's Lessons in Elementary Physiology is the most lucid statement of the facts of physiology yet presented. Among the best books of greater extent may be mentioned Foster's Textbook of Physiology; Stewart's Manual of Physiology; Kirke's Handbook of Physiology; Howell's American Textbook of Physiology; Verworn's General Physiology; Martin's The Human Body; and Hall's Textbook of Physiology. It goes without saying that the most recent edition of each must be used. See Blood, Circulation, Heart, Liver, Muscle, Nerves, Respiration.