ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



75 



The vagus fibres are medullated as far as the cardiac ganglia, while 

 the sympathetic fibres are non-medullated after leaving the third sym- 

 pathetic ganglion (Fig. 75c). Stimulation of the crescent still produces 

 inhibition, for weak doses of nicotine 

 do not paralyse the post-ganglionic 

 fibres. Nicotine is similarly em- 

 ployed to determine the cell stations 

 of all the nerve fibres of the auto- 

 nomic system (Langley). Too large 

 a dose of nicotine paralyses the 

 post-ganglionic fibres, renders the 

 contraction of the muscle slow. 

 At this stage stimulation of the 

 sinus will cause a series of rapid 

 beats due to the excitation of the 

 cardiac muscle ; this acceleration 

 shows as an after-effect a prolonged 

 period of diastole. Nicotine finally 

 arrests the heart-beat by poisoning 

 the muscle. 



Action of Chloroform and Ether. 

 Excise two frogs' hearts and 

 place each in a watch glass con- 

 taining 5 c.c. of Ringer's fluid. 

 To one add one drop of pure 

 chloroform and cover with another 

 watch glass. The heart will be- 

 come feeble, lose tone, and finally 

 stop beating. It will take about 

 ten times as much ether to pro- 

 duce the same effect on the other 

 heart. Chloroform is ten times 

 more potent a drug than ether. 

 The causation of death from chloro- 

 form is cardiac failure. In the 

 mammal the arterial pressure falls, 



and the vagus centre is rendered hyperexcitable by too concentrated 

 a dose of chloroform. Failure of respiration and syncope may result 

 from inhibition of the heart. 



Oil* 



