156 



PRACTICAL PHYSIOLOGY 



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10 



a fungus. It is used as an intoxicant in Siberia. It is excreted, 

 unchanged, in the urine, and it is stated that the urine is drunk 

 when the supply is short, and thus the intoxicant is handed on 

 from one man to another. 



Muscarine nitrate, C 5 H 15 N0 3 , is prepared artificially from cholin, 

 C 6 H 15 NO 3 . Cholin is one of the decomposition products of lecithin. 



Action of Nicotine. Dissect 

 out the vago-sympathetic and 

 record the beat of the heart by 

 the suspension method. Record 

 the effect of excitation of (1) the 

 vago-sympathetic, (2) the cres- 

 cent. Now apply to the heart 

 drops of a 0-1 per cent, solution 

 of nicotine. The frequency of 

 the heart is at first lessened and 

 then slightly increased, for the 

 nicotine firstly excites and 

 secondly paralyses the synapses 

 of the vagus fibres with the car- 

 diac ganglia. These ganglia con- 

 tain the cell stations of the vagus 

 fibres. Stimulation of the vago- 

 sympathetic trunk no longer 

 produces inhibition, but aug- 

 mentation and acceleration. 

 The cell stations of the sympa- 

 thetic fibres are in the third 

 sympathetic ganglion. 



The vagus fibres are medul- 

 lated as far as the cardiac gan- 

 glia, while the sympathetic fibres 

 are non-medullated after leaving 

 the third sympathetic ganglion 



(Fig. 148). Stimulation of the 

 crescent still produces inhibi- 

 tion, for weak doses of nicotine 

 do not paralyse the post-gang- 

 lionic fibres. Nicotine is simi- 

 larly employed to determine the 

 cell stations of all the nerve 

 fibres of the autonomic system 

 (Langley). Too large a dose of 

 nicotine paralyses the post-gan- 



glionic 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. 









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