This section is from the book "Human Physiology For The Use Of Elementary Schools", by Charles Alfred Lee. Also available from Amazon: Human Physiology, for the Use of Elementary Schools.
31. Many of the animal tissues are indebted for their physical properties to the water they imbibe. If they are deprived of this water, they are unable to perform their proper office and function, until they are again supplied with it. Hence one important reason why the system craves water, and why the want of it produces such distressing effects.
32. By the functions of man, we understand the operation of the various organs ; in other words, his vital actions. Life is made up of a constant series of these actions, from the period of birth to the moment of dissolution. Physiologists have attempted to define life ; but the best definition we can give is, that it is an assemblage of actions. Indeed, the essential nature of life is an impenetrable mystery, and not a proper subject for philosophical inquiry. As the fluids are as much endowed with life as the solids, it cannot be said that life is the " effect of organization ;" besides, a dead man has the same organization as when alive. It is, therefore, far better to confess our ignorance, and say with John Hunter,-" life is a property we do not understand."
33. All the actions or functions of the body are mutually dependent on each other. They constitute a circle, without beginning or end. The motion of the blood depends on the action of the heart and arteries ; the action of the heart and arteries depends on the presence of blood. The heart cannot act without the action of the lungs ; the lungs cannot act without the action of the heart. Neither lungs nor heart can act without the influence of the brain ; the brain would have no influence, were it not for the action of the lungs and heart.
34. Thus the steam of a steam engine works a bellows which blows a fire that produces the steam. It would be as difficult in this case, as in that of the animal functions to say, which of these might be easiest dispensed with. If we spare the bellows, the fire will not burn ; if we spare the fire, the steam will not be raised ; if we spare the steam, the bel lows will not be worked ; so that if we spare either fire, bellows, or steam, the machinery must stop. So it is in the human body.
35. The functions which fall within the scope of this work to notice, may be divided into three classes ; 1, vital; 2, nutritive ; and 3, sensorial. The vital functions are those which are every moment essential to preserve life. They also may be considered as three in number, viz : innerva. tion, circulation, and respiration; or the functions of the nervous system, those of the heart, and those of the lungs.
36. The nutritive functions preside over the growth and nutrition of the body. By their influence, the food is assimilated, and becomes a part of our structures ; while all the waste materials and worn out elements are expelled from the system. It thus embraces four functions; digestion, absorption, nutrition, and secretion.
37. The sensorial functions are sometimes called the functions of relation, because it is through them that we hold communication with the external world. They comprise the sensations, intellectual operations, and voluntary motions. It is the sensorial functions that raise man above all other animals. In proportion as they are more or less perfect, organized beings ascend or descend in the scale of existence. In the lower animals, they are limited to the circle of physical wants ; but in man, they confer moral and intellectual faculties, which are his noblest attributes.
38. These functions have the brain as their common centre. They can be improved to an almost indefinite degree by education and habit. We see this in the perfection which some of the senses acquire when others are lost; in the gigantic intellect of a Newton or a Locke, whose mental efforts at first were probably as weak as those of other men. In all such eases, individuals acquire superiority chiefly by education and constant practice.
How is living animal matter distinguished from dead ? What properties are possessed in common ? What are the phenomena of life owing to ? What developes the chick ? What properties does living matter possess ? What is understood by the sensitive powers ? -the motive ?-the alterative ? What characterizes animals provided with a nervous system ? How many kinds of sensibility are there ? What is meant by general sensibility ?-by special ? What is the common centre of sensibility ? What is perception ? What is organic sensibility ? Are the internal organs sensible to the presence of their contents ? How are such parts affected by disease ? What is con. tractility ? What element possesses it in a great degree ? How many kinds of contractility are there ? When is a limb said to be paralytic ? When in spasm ? What are the alterative powers ? What their use ? Is the body under the influence of chemical laws ? What are the physical properties of the animal tissues ? What office does elasticity perform ? Describe its operation in cartilages, arteries, etc. What are the uses of flexibility and extensibility in the animal body 7 What is imbibition ? Do the serous membranes absorb ? What experiments prove imbibition ? What are understood by the functions of man ? What is life ? Are the fluids alive as well as the solids ? Are the functions of the body dependent on each other? illustrate this dependence ? How are the functions divided ? What are vital functions ?-nutritive ?-sensorial ? What raises man above all other animals ?