The hypothesis discussed that the cavitation nuclei consist in gas bubbles. Due to surface tension, small bubbles would dissolve in a very short time. If the bubbles are larger than5×10−3 cm, or if the liquid is supersaturated, they may last longer or even be stable, but then no cavitation threshold exists.The hypothesis expressed that the nuclei are very small bubbles, stabilized by an organic skin, which mechanically prevents loss of gas by diffusion. The cavitation occurs when the skin breaks and the threshold is determined by the breaking strength of the film and the size of the bubble.