SAMUEL ERNEST POND 817 



Woods Hole, exhibited a smaller decrement in the rate of beat when 

 air had been bubbled through the solutions than when this procedure 

 was omitted. At Woods Hole the records showed better agreement 

 when the behavior of the hearts was studied in freshly made mix- 

 tures or in aerated mixtures than when similar solutions were used 

 which had stood in bottles for 2 days or more. 



Frog. — More extensive studies of the relationship between the elec- 

 trical conductivity of the surrounding medium and the propagation- 

 velocity of the contraction-wave have been made with the sartorius 

 muscle of the leopard-frog. Each muscle strip is mounted verti- 

 cally on a supporting apparatus; the muscle is stimulated electri- 

 cally at one end by minimal single shocks, and the contraction-wave 

 travels thence to the other end of the tissue along the parallel fibers. 

 The distances between the two points at which the wave has been 

 recorded vary between 1.5 cm. and 2.4 cm. Break-shocks are sent 

 into the tendinous end of the muscle through a platinum stimulating 

 electrode. The temperature during the experiments has been ad- 

 justed to 20°C. In some cases reported below the oxygen tension 

 has been increased by bubbling oxygen through the solutions. The 

 hydrogen ion concentration of all the mixtures is nearly 6.8. 



Tests made over long periods of time indicate that the sartorius 

 muscle of the frog is very resistant to the artificial conditions im- 

 posed in the experiments. Observations on muscles immersed in 

 Ringer's solution have been made at intervals during periods so long 

 as 96 hours, and toward the end of this time only a slight loss in the 

 propagation- velocity of the contraction-wave has been recorded. 

 The amplitude of the contraction-wave appears to decrease very 

 gradually during the first 2 days, and more rapidly during the third 

 and fourth days. In solutions of cane-sugar the irritability of the 

 tissue is soon lost completely; the time required with several changes 

 of solution varies from 20 to 30 minutes. Upon return to Ringer's 

 solution the irritability is restored within approximately 1 minute. 

 At 20°C. the normal rate of conduction of the tissue in Ringer's 

 solution is about 3 m. per second. In the Ringer-sugar mixtures 

 this rate decreases in close proportionality with the reduction of the 

 electrical conductivity until the concentration of the salts has been 

 reduced to about one-half the normal. In the range between the 



