The popular theory of "Negative Pressure", and its implications, conflict with the facts established by radiologists, divers, submarines and modern aviation. Though pressure in the body (belly or thorax) may at times seem negative, under ordinary circumstances it cannot be less than atmospheric, and in fact averages slightly more. The spontaneous movement of air from a pneumothorax or pneumoperitoneum, out into the atmosphere, proves this. The fact that elimination of a pneumoperitoneum or pneumothorax can take days or more, proves that pressure in the pleural or peritoneal cavities averages only slightly greater than pressure in the lymphatics/veins/atmosphere. Using Euclid's test for a hypothesis of examining its implications, one finds that negative pressure cannot exist in the body. Further, function of the contractile organs; heart, lungs, bowels, uterus, etc. are favored by pressure which stays close to neutral or zero, that is atmospheric. Atmospheric pressure is the bottom line, whereas "Negative Pressure" like "vacuum" is merely a theoretical concept.