COLLOIDS (Gr. Icoa6(571c , °glue-like"), substances, such as albumen and silicic acid, which, when combined with water in certain proportions, exhibit a gelatinous consistency. The word does not imply that there is any chemical resemblance among the bodies to which it is applied, the distinction between colloids and non-colloids being wholly physical. The terrn °colloid" was proposed by Thomas Graham, in 1861, to designate substances that are practically incapable of diffusion through porous mem branes. Substances such as salt, sugar and the mineral acids, which diffuse readily through such membranes, were called by him °crystal loids.'" Colloids and their properties are of special interest to students of biology, since the cells of all living organisms are made up of a mixture of chemical substances known as protoplasm, the structure of which is due to colloids. As Matthews has said, °the cell is not a single room in which all of the chemical processes occur in a higglety-pigglety manner, but is rather a well-organized chemical factory with different chemical processes occurring m different regions and in which substances are being elaborated as fast as they are required." This division of labor is made possible by the colloidal nature of the protoplasm. This col loidal structure is due to the fact that the or ganic substances of which it is in part composed have very large molecules. They have little en
env of translation and hence cohere. This colloidal nature of the products elaborated from the foods by the cell's chemical processes is what makes life possible. They are the true organizers of the cell's activities. Under the ultramicroscope one may see some of the col loidal particles dancing in the peculiar way known as the Brownian movements. These col loidal particles are the bearers of electrical charges, the opposite electrical charge being in the water which lies around the colloidal par ticles. There are electro-negative and electro positive colloids. They are usually very. small, varying from 1 to 100 25,000ths of an inch in diameter. The metal colloids are all electro negative, since they send out, in the presence of water, positive ion charges to the water. It is due to the electrical reactions taldng place in colloidal substances that the phenomena of life are largely possible. Energy is thus trans muted and made available for the life processes. In this transforming process certain substances termed enzymes accelerate these electrical re actions and hence are essential to the life processes. Consult Matthews, 'Physiological Chemistry" Bayliss, (Principles of General Physiology.>