1850s: Cholera rages through London and Paris, taking many lives and putting many people on guard against illness.

1890s: Because of better public hygiene, industrial towns have started to reduce the transmission of cholera and other contagious diseases. On a similar note, vaccines and xrays come into use.

Today: As modern medicine creates antibiotics and other medicines to combat disease, bacteria evolve, prompting the creation of newer medications.

1850s: With rare exception, middle-class women are expected to fulfill their traditional role of bearing and raising children. For those who are unmarried, serving as a governess in somebody else's home, helping to raise other people's children, is an acceptable option.

1890s: Women work more and devote less of their lives to bearing and rearing children, and their expectation of life increases.

Today: Women have many options for both work and family. Some choose not to...