with great facility. The epidermis or cuticle of the skin permits fluids to pass with difficulty. That water is taken up in considerable quantity, however, is proved by the fact, which has often been proved by experiment, that a man increases in weight by remaining for a considerable time in a warm bath.

30. The following experiments prove the nature of this process. (If we fill the intestine of a chicken with milk, and place it in water, we shall see the milk pass through its coats into the water, and the water will pass through in an opposite direction to supply its place. In the same manner, if a bladder be filled with hydrogen gas, and suspended in the air, in a short time it will be found to be mixed with atmospheric air, which has passed through its coats. The result of all the experiments on this subject seems to show, that when any cavity containing a fluid is immersed in another fluid less dense than the former, there is a tendency in the membrane to expel the denser, and absorb the thinner fluid.

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 opera

tion 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. Physiol. ogists 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 can. not 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 bellows 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: innervation, 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 limit. ed 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 cases, individuals acquire superiority chiefly by education and constant practice.

Questions. How is living animal matter distinguished from dead? What properties are possessed in common? What are thè 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 contractility? 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, &c. What are the uses of flexibility and extensibility in the animal body? 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 ?

CHAPTER VIII.

RELATION OF ANIMAL BODIES TO HEAT, LIGHT, AND

ELECTRICITY.

1. The relations which animal bodies have to heat, light, and electricity, are highly interesting, and worthy of particu lar notice. To a certain extent, all animal bodies have the power of regulating their own temperature. Many of them develope electricity; and some of them, like the lightningbug, and other insects, can produce light. These are singular properties of living animal matter.

2. The heat of animal bodies is produced within themselves. It is not received from without, nor can it be; as the natural temperature of the body is near 100 degrees; even when the temperature of the surrounding air is below How this is produced we shall inquire when we come

zero.

to treat especially of animal heat.

3. Plants have a lower temperature than animals, and the higher animals are in the scale of organized beings, so much the more animal heat do they produce. Thus the temperature of what are called the cold-blooded animals, such as fishes, is not much above that of the water in which they live; and although they do not often freeze to death in the winter, yet they become so torpid as to be incapable of motion.

4. It is a favourite sport in New England in the winter season, to hunt, on skates, for the pickerel, and other fish, which abound in the lakes and ponds; and when found to take them, by cutting through the ice with a hatchet; and to spear them by torchlight at night. Now had they the faculty of producing animal heat, like quadrupeds, or birds, or man, they would not be rendered torpid and incapable of motion by cold.