NERVOUS SYSTEM 157 



(5) Nerve extracts also relax fow^l rectal caecum preparations 

 (Ostlund, 1954). 



(6) Adrenaline effects on the gut are increased by ephedrine, 

 and reduced by ergotoxin. 



(7) Although the evidence is inconclusive Blaschko and 

 Himms (1953) believe the presence of an amine oxidase in the 

 ventral nerve cord is very likely. 



Von Euler (1948) and Ostlund (1954) both suggest, how- 

 ever, that adrenahne is not present alone, but is accompanied 

 by noradrenaline. Ostlund could not confirm this by chromato- 

 graphy because of lack of materials. Von Euler (1961), how^ever, by 

 use of a fluorimetric technique has shown that adrenaline is 

 present to the amount of 0-003 fj^glg, and noradrenaline 0-015 /xg/g 

 in Lumbricus terrestris. 



Giant Fibres 



In transverse sections of the nerve cord of the oligochaetes it is 

 to be noted that dorsally there lie three large areas which are in fact 

 huge axons. These are the giant fibres. They extend the whole 

 length of the body from the cerebral ganghon to the pygidium, and 

 in each segment several large cells send their axons into these 

 fibres. There is a median large fibre, flanked by two smaller lateral 

 fibres. In each segment two pairs of giant cells send processes to 

 the median fibre, and the lateral fibres are connected to one another 

 by transverse fibres. Branches are believed to be given to the motor 

 neurones in each segmental nerve. Two rather smaller giant fibres 

 lie ventrally in the nerve cord, but they remain unknown physio- 

 logically (Stough, 1926, 1930; Smallwood and Holmes, 1927). 



These giant fibres are concerned in the rapid withdrawal or 

 "startle" response of the earthworm. This has been shown many 

 times by experiments involving cutting, regeneration, embryonic 

 development and blocking with a number of depressant drugs 

 (Prosser, 1933). Stough (1930) believed that the giant fibres were 

 polarized and conducted in one direction only. By cutting the 

 median fibre he found that anterior stimulation initiated muscular 

 responses as far back as the cut but not beyond. Posterior stimula- 

 tion caused the whole animal to contract. If he severed the two 

 lateral fibres anterior stimulation invoked contraction of the whole 

 animal, but posterior stimulation produced contraction only up to 



