The successful application of the hot wire anemometer to the study of the coronary circulation (see Anrep, Davis, and Volhard, 1931) incited us to use the same method in a series of experiments upon the circulation in the skeletal muscle. Until recently, the blood flow through muscles was measured either by direct observation of the outflow of blood from a cut muscle-vein or with the help of various mechanical "Stromuhrs" (Sczelkow, 1863; Ludwig and Schmidt, 1868; Sadler, 1869; Gaskell, 1877). These methods allowed only a coarse registration of average blood flows in comparatively long intervals of bearing upon the problem. According to Gaskell, there is a large increase in the venous outflow from the muscle at the beginning of a tetanic contraction; with the continuation of the tetanus, the outflow is rapidly and greatly diminished and frequently it even stops; after the end of the tetanus, the outflow again increases decidedly above normal, and returns to the normal level only after a considerable interval of time. Gaskell considered that the initial increase and the subsequent diminution of the venous outflow during the tetanus was due to a mechanical diminution of the venous outflow during the tetanus was due to a mechanical compression of the blood vessels. The large increase, which he observed as an after-effect of the tetanus, he regarded as due to the action of potent vasodilator chemical substances which accumulated within the muscle during its contraction. A more exact determination of the time relations between the contraction and the changes in the venous outflow from the muscle has been attempted by Burton-Opitz (1903) with the help of Hürtle's Stromuhr. His experiments confirmed the observations of Gaskell, except that he failed to observe the prolonged increase of the blood flow after the termination of the tetanus. He described only a small outrush of blood immediately following the relaxation; this increase in the flow lasted, however, only a 1/2 to 1 second. On comparing the blood flow during tetanus, or during a series of single contractions with the resting blood flow, Burton-Opitz found a considerable decrease in the first case and an increase in the second. Unlike Gaskell, he ascribes both effects the tetanus, and to a massaging action of the single contractions. In the latter case, the increase of the blood flow was found to be roughly proportional to the volume of blood expelled from the muscle during each contraction. Verziar (1912) also observed an arrest of the venous outflow during each tetanic contraction.