organism, as the surface area of just the front 2/3 of the organism has an effect on the drag. The resistance to the motion of an approximately stream-lined solid through a fluid can be expressed by the formula: Cfρ(total surface)V2/2, where: V = velocity ρ = density of fluid Cf = 1.33R − 1 (laminar flow) R = Reynolds number The Reynolds number R is given by R = VL/ν, where: V = velocity L = axial length of organism ν = kinematic viscosity (viscosity/density) Notable Reynolds numbers: R < 0.5×106 = laminar flow threshold R > 2.0×106 = turbulent flow threshold Scaling also has an effect on the performance of organisms in fluid. This is extremely important for marine mammals and other marine organisms that rely on atmospheric oxygen for respiration and survival. This can affect how fast an organism can propel itself efficiently or how long and deep it can dive. Heart mass and lung volume are important in determining how scaling can affect metabolic function and efficiency. Aquatic mammals, like other mammals, have the same size heart proportional to their bodies. In general, mammals have hearts about 0.6% of their total body mass: , where M is the body mass of the individual. Lung volume is also directly related to body mass in mammals (slope = 1.02). The lung has a volume of 63 ml for every kg of body mass, with the tidal volume at rest being 1/10 the lung volume. In addition, respiration costs with respect to oxygen consumption is scaled in the order of . This shows that mammals, regardless of size, have similarly scaled respiratory and cardiovascular systems and the same relative amount of blood: about 5.5% of body mass. This means that for similarly designed marine mammals, a larger individual can travel more efficiently, as it takes the same effort to move one body length. For example, large whales can migrate far distance in the oceans and not stop for rest. It is metabolically less expensive to be larger in body size. This goes for terrestrial and flying animals as well: smaller animals consume more oxygen per unit body mass than larger ones. The metabolic advantage in larger animals makes it possible for larger marine mammals to dive for longer durations of time than their smaller counterparts. That the heart rate is lower means that larger animals can carry more blood, which