Gerry Smith's thoughtful survey in his book Satiation (1998) outlined the established principles of gastric and intestinal satiation and delineated several questions still requiring clarification. Experiments since the time of the review have addressed some of these questions. A synthesis of the principles outlined in the Gerry Smith survey and the subsequent experimental results indicates that the direct controls, or neural feedback signals from the GI tract, that limit meal size consist of gastric volumetric signals and intestinal nutritive signals. The two types of negative feedback synergize in the control of feeding, and both are carried by vagal afferents.