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PRINCIPLES OF GENERAL PHYSIOLOGY 



In a later paper bv Sherrington and Owen (1911) the question is discussed further, but the 

 impossibility of a definite decision is pointed out until we have a nerve which can be proved 

 to contain no afferent excitatory fibres whatever. 



Chloroform is well known to be, pharmacologically, a general antagonist to 

 strychnine ; it is not unexpected, therefore, to find that its action on nerve 

 processes is the reverse of that of strychnine. I showed (1908, 2) that it converts 

 the excitatory component of a vasomotor reflex into an inhibitory one. That is, 

 the rise of pressure produced by a nerve which excites the vaso-constrictor centre 

 is converted into a fall. Examples of this fact are given in Fig. 128, from a 

 paper by Mathison (1912), and Fig. 129 from one of mine. Similarly, Sherrington 

 and Sowton (1911, 2) showed that the reflex contraction of the vasto-crureus, 

 evoked by stimulation of the popliteal, internal saphenous or genito-crural nerve, 

 was converted into inhibition by the administration of chloroform. 



Reversals of this kind can be brought about without the influence of drugs, as 

 shown more particularly by Magnus (1909). The direction of the movement of the 

 tail of a spinal cat, when the tip is pinched, varies with the position in which it hangs. 

 The movement is always towards the stretched side, so that the same afferent impulse 

 produces, in one position, excitation of those muscles which are inhibited in the opposite 



position. The condition 

 of the centre must be 

 changed by receipt of 

 afferent impulses from 

 the stretched muscle. 



Returning to the 

 action of chemical 

 agents, Dale, Laid law, 

 and Symons (1910) 

 describe how stimula- 

 tion of the vagus in the 

 cat, under the effect of 

 nicotine, causes marked 

 acceleration instead of 

 slowing of the heart. 

 This may be due to 

 earlier paralysis of the 

 inhibitory fibres than 

 of supposed accelerator 

 fibres, normally masked. 

 Or it may be a reversal 

 of the function of the 

 inhibitory fibres. In the 



latter case, we should have an instance of reversal of a peripheral muscular 

 mechanism. The authors named are inclined to favour the former hypothesis, 

 but it does not seem probable, a priori, that fibres acting in the same way as the 

 sympathetic supply of the heart should be present in a cranial nerve. 



Again, Dale and Laidlaw (1911) found that, after a dose of cytisine, the 

 alkaloid of laburnum seeds, stimulation of the chorda tympani nerve in the cat 

 produces no secretion while the stimulus lasts, but is followed by a copious flow. 

 A renewed stimulation, during this after-flow, nearly stops it, but the course is 

 resumed after the stimulation ceases. 



The authors suggest no explanation, but it seems to me, although I admit that the 

 suggestion is purely hypothetical, that, if we regard the action of strychnine and of chloro- 

 form as actually reversing the sign of the effect on a nerve cell, why should we not accept 

 the possibility of similar reversal in peripheral inhibition and excitation in smooth muscle 

 and heart ? If this be so, the above result on the salivary secretion might easily be explained 

 by conversion of the normal vaso-dilator action of the chorda tympani into a vaso-constrictor one, 

 the diminution of flow being then due to failure of blood supply. This hypothesis might be 

 tested by determining the rate of blood flow under the conditions of the experiment. 



Langley (1911) finds that, after nicotine or curare, the normal contraction of 

 the bladder produced by stimulation of the sacral nerves is followed by inhibition, 



FIG. 128. REVERSAL OF VASO-CONSTRICTOR REFLEX BY CHLOROFORM. 



Stimulation of central end of hypoglossal nerve in the rabbit. 



Left-hand tracing under urethane alone. 



Right-hand tracing under 3 per cent chloroform in addition. 



(Mathison, 1912, Fig. 2.) 

 (By the kindness of Dr Ninian Bruce.) 



