Homicide is defined as an index of individual, nonrational violence. Homicide is considered to be one of the firmest indices of criminal behavior because it is less subject to labeling vagaries and because most homicides become known to the police; however, neither assumption was true in the 19th century, and the number of homicides was generally underestimated. The estimate of homicides is based on grand jury indictments. Lack of forensic techniques and detectives and public aversion to labeling crimes as homicides caused many crimes to be labeled as accidents or suicides. A socialization model -- the suicide-murder ratio -- is useful in more accurately tracing homicide rates. This model suggests that those inclined toward murder tent to be reckless, spontaneous, and impulsive, while potential suicides are trained to be rational and cooperative. Socialization processes occurring during the latter part of the 19th century inlcuded the development of public schools and a structured industrial work environment. These developments tended to reduce reckless, impulsive behavior and the homicide rate, while creating conditions favoring increases in the suicide rate. An examination of the murder rate in Philadelphia indicated that a significant decrease occurred during the public school development and industrialization period which occurred during the last hals of the 19th century. Increases in homicide since the late 1950's represent the postindustrial era with declining occupational opportunities for the unskilled and increasing levels of frustration, particularly among blacks.