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Twist ye, twine ye! even so Mingle shades of joy and woe, Hope and fear, and peace and strife, In the thread of human life. All molecules in a living organism serve a purpose, and we cannot say that a particular type is more important than any other. Nevertheless, it would be difficult to identify substances that play more varied and central roles than do the biopolymers. They contribute to the mechanical structure, and in the animal kingdom they provide the means of motion. They facilitate transport of smaller chemical units and mediate the chemical interaction between molecules, the biopolymers that serve this catalytic function being the proteins known as enzymes. There are biopolymers that form the immunological system and others that are involved in the mechanism of tissue differentiation. With so many functions to be fulfilled, we should expect to find many different types of these ubiquitous molecules, and this is certainly the case. It is believed, for example, that there are several hundred distinct enzymes within each cell of a higher organism such as a mammal. Even the task of perpetuating and translating the genetic message is entrusted to biopolymers. The body of a typical mammal is mostly water – about 65% by weight in fact – but of the solid components no group is better represented than the proteins; they make up about 15% of the total weight. [ABSTRACT FROM AUTHOR]

All things began in order, so shall they end, and so shall they begin again; according to the ordainer of order and mystical mathematics of the city of heaven. Until now, our discussion has concerned isolated atoms and clusters of very few atoms. Considering that a single cubic centimetre of a typical piece of condensed matter, a block of stainless steel for example, contains approximately 1023 atoms, we see that there is still a long way to go in the description of actual substances. We must now inquire how large numbers of atoms are arranged with respect to one another, so as to produce the great variety of known materials. It will transpire that the observed arrangements are dictated both by the forces between atoms and the prevailing physical conditions. Before going into such details, however, it will be useful to examine the simple geometrical aspects of the question. It is frequently adequate to regard atoms as being spherical. The two-dimensional equivalent of a sphere is a circle, so we can begin by considering the arrangement of circles on a piece of paper. The circles could be drawn at random positions, well spread out and with close encounters occurring only by occasional chance. This is a reasonable representation of the instantaneous situation in a simple monatomic gas. A variant of this drawing would replace the single circles by small groups of circles, and we would then have a molecular gas. [ABSTRACT FROM AUTHOR]