82 ADRENALIN IN ANNELIDS 



rized leech had no effect, but in the decapitated animal caused marked 

 slowing of the rate. The posterior nerve therefore contains fibers 

 which are inhibitor to the vascular muscle. The acceleration effect 

 produced by stimulation of the anterior nerve is abohshed by the injec- 

 tion of ergotoxin. The vascular system is thus definitely under the con- 

 trol of the central nervous system, the arrangement being a segmental 

 one, and the length of the vessel lying in any segment being controlled 

 by cells in the ganglion of that segment. The accelerator fibers run 

 in the anterior nerve, and their action is abolished by ergotoxin in the 

 same way as is the case with the mammalian sympathetic system. 

 These accelerator fibers have been definitely traced to the muscle 

 and are very probably the processes of the chromaffin nerve cells, 

 which therefore control the vascular muscle in the leech in a similar 

 way to its control in the vertebrate by the sympathetic system. The 

 inhibitor fibers run in the posterior nerve and are also processes of 

 cells in the central ganglion. Their action is abohshed by curare. 

 They control the vascular muscle in a manner strictly comparable to 

 the control of the vertebrate heart by the vagus nerve. 



The nerve supply of the vascular muscles is therefore a double one 

 which is strictly comparable to the double supply of the vertebrate 

 heart by the sympathetic and vagus systems. The power of rhyth- 

 mical contraction is an intrinsic property of the vascular muscle 

 itself, to which the two nerves act as regulators. In the primitive 

 form found in annelids, the heart beat is therefore myogenic in origin, 

 but is regulated by the control of the nervous system. 



The action of adrenahn was tried both on the longitudinal and 

 circular voluntary muscles and on the vascular muscles. Experi- 

 ments on the voluntary muscles of the leech were difficult, and were 

 supplemented by similar experiments on Lumbricus. No effect could 

 be obtained in these muscles in either animal by the application of 

 adrenalin if it was applied in neutral solution; with the usual acid 

 solution in the form of hydrochloride the acidity of the solution was 

 always sufficient to cause a contraction. Adrenahn borate was found 

 to be a form suitable for the purpose. It was apphed directly to a 

 lateral vessel of the leech, after exposing it under Ringer's solution, 

 by injection into the loose tissue lying around the vessel. The effect 

 of the injection of one drop of a solution in Ringer of adrenahn borate 



