68 



LEECHES 



concentration facilitates relaxation without affecting the sensitivity 

 to acetylcholine, so that the best method of preparing leech muscle 

 for assay of acetylcholine is to treat it with morphine and eserine 

 sulphate (Murnaghan, 1958). During electrical stimulation 

 acetylcholine is released into the surrounding fluid and it therefore 

 seems likely that it has been produced at the neuromuscular junc- 

 tion, and that this is the normal mechanism for inducing contrac- 

 tion (Bacq and Coppee, 1937). Cholinesterase is present in both 

 the muscles and the ventral nerve cord and presumably hydrolyses 

 the acetylcholine as soon as it has done its work. Eserine inhibits 

 cholinesterase, so this accounts for its effect of increasing the 

 response to stimulation. 



The rate of action of leech longitudinal muscle is slow, con- 

 sidering that it is concerned with locomotion, escape reactions and 

 attachment to host. Schwab (1949) studied the time constants of 

 dorsal longitudinal muscle of Haemopis. Table 2 shows that it is 



Table 2. Time Constants of Various Muscles 



much slower than vertebrate limb muscle, e.g. frog sartorius, and 

 is more nearly comparable with such muscles as Pecten slow 

 adductor or cat diaphragm. Similar results were obtained with 

 the muscle of Hirudo by Lapicque and Veil (1925) who compared 

 them* with the muscles of the body wall of an earthworm. They 



