Scientific advance is never uniform

Scientific advance is never uniform nor simultaneous along an entire front. It occurs rather at different times, in varying ways and in relation to specific areas of knowledge. In some instances, what is required is the discovery and definition of elementary data; in others, where a solid knowledge of elementary factors already exists, fruitful advance can occur through the creation and application of an intergrating concept, or by attacking a more complex problem and contributing to its solution. All these aspects may be ob-served in relation to public health during the period under discussion.