Physiology and Hygiene for Secondary Schools

it up? What general work do these carry on and upon what basis do they practice the division o

the cells and the intercellular materia

s suitably prepared and carefully examined with this instrument, at least two classes of materials can be made out. One of these consists of minute particles, called cells; the other is a subst

ls that form groups are attached to, and are more or less dependent upon, one another. In the first condition are [pg 014] found the very lowest forms of life. In the second, life reaches its greatest development. The body of man

e and composition are unknown, because any attempt to analyze it kills it, and dead protoplasm is essentially different from living protoplasm. It is known, however, to be a highly complex substance and to undergo chemical change readily. It appea

he cell is looked upon as a complex body having several distinct parts. At or near the center is a clear, rounded body, called the nucleus. This plays some part in the nourishment of the cell and also in

leus. 3. Attraction sphere. 4. Food particles and waste. 5. Cell-wall

the cytoplasm, in many cells, is a thin outer layer, or membrane, which affords more or less protection to the contents of the cell. This is usually referred to as the cell-wall. A fourth part of the cell is also described, being called the attract

urposes. Working through the tissues, they build up the body and carry on its different activities. They are recognized on this account as the units of structure and of function, and

the effect of increasing the size of the entire body, and this is one way by which they cause it to grow. There is, however, a fixed limit, varying with different cells, to the size which they attain, and this is quite low. (The largest cells are scarcely visible to the naked eye

process begins with the division of the attraction sphere, t

wever, that the act of separation is preceded by a series of changes in which the attraction sphere[pg 017] and the nucleus actively participate, and that, as a result of these changes,

ll reproduction is supposed to cease except where the tissues are injured, as in the breaking of a bone, or where cells, like those at the surface of the skin, are sub

rbles covered with water, suggesting t

s also an essential part of the protoplasm. Deprived of water, cells become inactive and usually die. Aquatic surroundings are provided for the cells of the body through a liquid known as the lymph, which is distributed throughout the intercellular

derived from the lymph, the cells carry on three well-defined

of taking water, food, a

ddition of the absorbed materials to the protoplasm. Thr

s as have been formed in the cells. These are passed

ion are performed by all classes of cells. They are, on

they can do only to a limited extent. This is spoken of as the special work of cells. Examples of the special work of cells are found in the production of motion by muscle cells and in the secretion of liqui

nded by the intercellular mate

ellular material which they contain, the difference being due to these cells.[pg 019] In the connective tissue they deposit the fibrous material so important in holding the different parts of the body together. In the cartilage they produce the gristly substance which forms by far its larger portion (Fig. 7). In the bones they dep

e cells form the tissues and the tissues form the organs. This arrangement enables the special work of different kinds of cells to be combined in the work of the organ as a whole. This is seen in the hand which, in grasping, uses motion supplied by the muscle cells, a controlling influence suppl

e cells to form the tissues. A

ssues in the organ. Each organ cont

re is a definite arrangemen

and systems, together with the structures

toward which all the activities of the body organization are directed? This purpose will naturall

come scattered, a fact which is verified through everyday observation. Though the nature of life is unknown, it may be looked upon as the organizer and preserver of the protoplasm. But in preserving the protoplasm it also pres

ey be relieved of such wastes as they form.[pg 021] This double purpose is accomplished through the agency of an internal nutrient fluid, a portion of which has already been referre

oxygen must be continually added to this fluid, and waste materials must be continually removed. This is not an easy task. As a matter of fact, the preparation, distribution, and purificati

nds for handling things, the eyes for directing movements, etc. That the great needs of the body are supplied from its surroundings are facts of common experience. Food, shelter, air, clothing, water, and the means of protection are external to the body and form a

the body is thus seen to resolve itself natura

aining in the body a nut

its surroundings as will enable it to secure materia

ere, and includes the work of the external organs-the organs of motion and of locomotion and the organs of special sense. These problems are closely related, since they are t

nt activities. The tissues are groups of like cells. By certain general activities the cells maintain their existence in the tissues and by the exercise of certain special activities they adapt the tissues to their purposes in the body. The body, as a cell organiz

ick wall, to what do the separate bricks corr

ypical cell, locating and

the body to grow? Describe

fer from their special work? Define absorption, e

e-celled animal, living in water, to the c

vironment"? How does man's envir

ssity for a nutrien

fe necessarily the chief aim of

ain problems in th

TICA

with a little water on a glass slide. Place a cover-glass on the same and examine with a compoun

power of microscope. (Suitable slices may be cut, with a sharp razor, from the cartilage found at the end of the

es of elder pith, potato, and the stems of growing

idermis of a frog's skin. Examine it first in its natural condition, and th

icroscope. Note the variety and relative size of the different things moving about. The forms most

have been suitably prepared and mounted for microscopic study, using low and high powe

g