General Anatomy or Histiology: The Animal Cell Part 1

All tissues and organs of which the body is composed were originally developed from the ovum and are made up of similar bodies, or cells. Every cell of a higher organism must contain two things: protoplasm and a nucleus. Other parts of a cell are optional, such as the cell wall or the centrosphere.

Protoplasm, also called cytoplasm, is composed chiefly of things of proteid nature, and is of a semi-fluid, viscous substance. It appears either as a hyaline (homogeneous and clear) substance, also known as spongioplasm, or exhibits a granular appearance due to fact that protoplasm consists of a honeycombed reticulum with a homogeneous substance within its meshes (this appearance is known as hyaloplasm). Generally the appearance of granules is caused by the knots of the network being mistaken as such, but protoplasm also often contains true granules, whether of proteid nature, most likely essential to the cell, or of fat or pigment, which likely come from outside the cell. The size and shape of the meshes of spongioplasm vary between cells and within the cells, and can become a cell wall. The amount of spongioplasm and hyaloplasm varies within cells, with younger cells generally containing more hyaloplasm and older cells more spongioplasm.

Protoplasm has interesting manners of movement and nutrition. To move, it either thrusts a bit of itself outward and draws the rest of the cell toward it (known as amœboid movement), or vibrates hair-like processes from the surface of the structure to move (known as ciliary movement). It gains nutrition through attracting itself to the materials necessary to its growth and maintenance from the surrounding matter. When foreign substances come in contact with the protoplasm, they are drawn within it, and then either kept or extruded again.

The nucleus is a spherical or oval form embedded in the protoplasm and surrounded by a wall known as the nuclear membrane, whose contents are known as the nuclear substance. The size of the nucleus has no relation to the size of the cell. The nuclear substance consists of a homogeneous material likely of the same nature as the hyaloplasm of the cell and of a stroma or network of filaments arranged in a reticular manner and called the chromoplasm or intranuclear network. The filaments are called chromatin because they stain readily with certain dyes, and the homogenous substance is called achromatin because it does not. The nuclear substance also includes one or more highly refracting bodies called nucleoli, which may be considered pseudo-nucleoli (local condensations of the chromoplasm, irregular in shape) or true nucleoli (which differs in both nature and chemical composition from pseudo-nucleoli).

The nuclear substance also differs chemically from ordinary protoplasm in a number of ways: First, in containing nuclein, second in its power of resisting the action of acid and alkalies, and third in its different reaction to certain dyes.