“The mechanism of conduction and coördination in the heart,with special reference to the heart of Limulus”

I. The Rate of Conduction. — It is advocated, chiefly by Engelmann, that the rate of conduction of an impulse in the heart is too low (20 cm. to 30 cm. per sec. in the frog; 2 m. to 4 m. per sec. in the dog) to take place in the nervous tissue. The slow conduction in the heart is thus construed as an argument in favor of the myogenic theory. This is based on the erroneous assumption that all nervous paths in the same animal conduct with the same, or practically the same, rapidity. The author has shown that this is not the case even for the motor nerves to the striated muscles. On the contrary the rate of conduction in the nerve stands in direct relation to the rapidity of contraction of the muscle supplied by the nerve. 1 On this principle one would expect the rate of conduction in the intrinsic nervous plexuses of the alimentary tract and of the heart of a vertebrate to be as much slower than that in the motor nerves to the skeletal muscles, as the contraction of heart-muscle and muscle of the digestive tract is slower than that of skeletal muscle. The rate of conduction in the intrinsic nerves of the vertebrate heart has not yet been determined. In the heart of Limulus, this can be done by the ordinary graphic method. The author has shown that in the heart of Limulus the rhythm is neurogenic, not myogenic, and that the conduction and coördination take place in the nervous and not in the muscular tissue. 2 The proofs of these conclusions are demonstrative. The author has lately measured the rate of conduction in the intrinsic heart nerves of this animal and has found it to be 40 cm. per second. The rate in the motor nerves to the limbs as found by the author is 325 cm. to 350 cm. per second.