Man's physical universe

xanabras

UNIT X

SECTION 2

FOODS ARE THE RAW MATERIALS OF LIVING

ORGANISMS

Introduction.

No matter what type of cell is examined under the microscope (a

drop of blood the size of a pin's head contains millions of cells), it will

always be found to contain a slimy, viscous, semifluid material called

"protoplasm," which is the living material itself. This protoplasm and

the cell walls in which it is retained are colloidal materials. The processes

by which cells, obtain foods, change it into new forms, discard

waste products, and reproduce themselves are likewise colloidal in

nature. For that reason the study of colloids was reserved for this

Section, which is devoted to the study of foods.

Matter in the Colloidal State Is the Vehicle of Life.

In 1861 Thomas Graham found that certain substances in a solution

would pass through a parchment paper while others would not. The

former he called crystalloids and the latter colloids. It is only within

the last twenty-five years, however, that the information has been

obtained which shows that nearly every kind of matter may assume

the colloidal state. The properties of colloids are more the result of

the size of the particles than the nature of the particles dispersed. For

that reason the colloidal state is considered to be a physical state of

matter.

Matter in the Colloidal State Exhibits Several Distinctive Properties.

/. Brownian Movement. In 1827, long before Graham had coined

the term "colloid," another Scotch scientist, Robert Brown, noticed

peculiar movements of pollen grains in water as he examined them

under the microscope. This constant zigzag motion, characteristic of

all colloids, was later called the Brownian movement, in honor of the

man who first observed it.

2. Tyndall Effect. This effect was named after the eminent Irish

scientist, John Tyndall, who observed that the path of a beam of light

725

More magazines by this user
Similar magazines