114 



PRACTICAL PHYSIOLOGY 



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. 113). 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, and 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 con- 

 siderably more ether to produce 

 the same effect on the other heart. 

 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 result from 

 inhibition and poisoning of the heart. 



Alcohol, - 



Ether, 



Chloroform, 



By Molecules. 



8 

 100 



By Weight. 

 1 

 5 

 40 



The relative physiological powers of alcohol, ether and chloroform. 



By Volume. 



5 



75 

 (Waller.) 



