A1/B1, A2/B2, A3/B3
and so forth. The use of balanced sentences intensifies the effect of the comparison. In the second paragraph, primitive medicine is first described and then modern medicine is described by contrast. The pattern here could be diagrammed thus:
A1 A2 A3/B1 B2 B3.
The use of a transitional device ("On the other hand") is very important to signal the shift in this pattern of comparison.
[1.] One of the masses is built of cut stone, the other of poured concrete. One took 50,000 men twenty years to build, the other will take 5,000 men six years, in a task not only three times greater but vastly more complex and dangerous. Both structures relied on the labor of those who would otherwise have been unemployed. Egyptian peasants in the off season built Cheops; American workingmen and engineers shelved by a great depression are building Grand Coulee. Pyramids were houses for the dead. Dams are centers of energy for the living. It is better, I think, to live in the age of the Great Dams than in the age of the Great Pyramids.
[2.] There are two philosophies of medicine: the primitive or superstitious, and the modern or rational. They are in complete opposition to one another. The former involves the belief that disease is caused by supernatural forces. Such a doctrine associates disease with sin; it is an aspect of religion which conceives diseases as due to certain forms of evil and attempts to control them by ceremonial and superstitious measures or to drive them away by wishful thinking. On the other hand, rational medicine is based on the conception that disease arises from natural causes; it associates sickness with ignorance. Civilized man tries to control the forces causing disease by material, not spiritualistic, means; he does not view disease as supernatural or the outcome of sin against moral laws, but rather as resulting from the violation of sanitary laws. He recognizes that knowledge is the sole means of preventing it. The measures he relies upon both to prevent and cure disease are those which have resulted from scientific investigation and which have been proved to be effective by experience.