32 (202) Society for Experimental Biology and Medicine. 



mutual contamination of characters in hybrids justifies the warn- 

 ings given by breeders as to loss of characters in hybridization, and 

 the care that they exercise to maintain pure races. 



15 (107). " The mechanism of conduction and coordination in 

 the heart, with special reference to the heart of Limulus " : 

 A. J. CARLSON. (Presented by RUSSELL BURTON-OPITZ.) 



I. The Rate of Conduction. — It is advocated, chiefly by Engel- 

 mann, 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 conduc- 

 tion 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 

 condtiction 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 coordina- 

 tion 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. That is to say, the rate of conduction in 

 the nervous plexus in the heart is from eight to ten times sloiver than 

 in the peripheral motor nerves. 



'Carlson: American Journal of Physiology, 1904, x, p. 401. 



'Carlson: American Journal of Physiology, I904~'05, xii, p. 67; also, p. 471. 



