TURCK'S METHOD THEORY OF REFLEX ACTION. 64 1 



Tiirck's method of testing the reflex excitability of a frog is the following : A 

 frog is pithed, and after it has recovered from the shock, its foot is dipped into 

 dilute sulphuric acid [2 per 1000]. The time which elapses between the leg being 

 dipped in and the moment it is withdrawn is noted. [The time may be estimated 

 by means of a metronome, or the movements may be inscribed upon a recording 

 surface. The time which elapses is known as the " period of latent stimulation."] 



This time is greatly prolonged after the optic lobes have been stimulated with a crystal of 

 common salt or blood, or after the stimulation of a sensory nerve. 



Setschenow distinguished tactile reflexes, which are discharged by stimulation of the nerves 

 of touch ; and pathic, which are due to stimulation of sensory (pain-conducting) fibres. He and 

 Paschutin suppose that the tactile reflexes are suppressed by voluntary impulses, and the pathic 

 by the centre in the optic lobes. 



Theory of Keflex Movements. The following theory has been propounded to account for the 

 phenomena already described : It is assumed that the afferent fibre within the grey matter of 

 the spinal cord joins one or more nerve-cells, and thus is placed in communication in all direc- 

 tions with the network of fibres in the grey substance. Any impulse reaching the grey matter 

 of the cord has to overcome considerable resistance. The least resistance lies iu the direction 

 of those efferent fibres which emerge in the same plane and upon the same side as the entering 

 fibre. Thus, the feeblest stimulus gives rise to a simple reflex, which generally is merely a 

 simple protective movement for the part of the skin which is stimulated. Still greater resist- 

 ance is opposed in the direction of other motor ganglia. If the reflex impulse is to pass to 

 these ganglia, either the discharging stimulus must be considerably increased, or the resistance 

 within the connections of the ganglia of the grey matter must be diminished. The latter 

 condition is produced by the action of the above-named poisons, as well as during general 

 increased nervous excitability (hysteria, nervousness). Thus, extensive reflex spasms may be 

 produced either by increasing the stimulus, or by diminishing the resistance to conduction in 

 the spinal cord. Those conditions which render the occurrence of reflexes more difficult, or 

 abolish them altogether, must be regarded as increasing the resistance in the reflex arc in the 

 cord. The action of the reflex inhibitory mechanism may be viewed in a similar manner. 



The fibres of the reflex arc must have a connection with the reflex inhibitory paths ; we must 

 assume that equally by the reflex inhibitory stimulation resistance is introduced into the reflex 

 arc. The explanation of extensive co-ordinated movements is accompanied with difficulties. It 

 is assumed, that by use and also by heredity, those ganglionic cells which are the first to receive 

 the impulse are placed in the path of least resistance in connection with those cells which 

 transfer the impulse to the groups of muscles, whose contraction, resulting in a co-ordinated 

 purposive movement, prevents the body or the limb from being affected by any injurious 

 influences. 



Pathological. Anomalies of reflex activity afford an important field to the physician in the 

 investigation of nervous diseases. Enfeeblement, or even complete abolition of the reflexes 

 may occur : (1) Owing to diminished sensibility or complete insensibility of the afferent fibres ; 

 (2) in analogous affections of the central organ ; (3) or, lastly, of the efferent fibres. "Where 

 there is general depression of the nervous activity (as after shocks, compression or inflammation 

 of the central nervous organs ; in asphyxia, in deep coma, and in consequence of the action of 

 many poisons), the reflexes may be greatly diminished or even abolished. 



[Reflexes. The physician, by studying the condition of the reflexes, can form an 

 idea as to the condition of practically every inch of the spinal cord. There are 

 three groups of reflexes, (a) the superficial, (b) the deep or tendon, (c) the organic 

 reflexes.] 



[The superficial or skin reflexes are excited by stimulating the skin, e.g., by 

 tickling, pricking, scratching, &c. We can obtain a series of reflexes from below 

 as far up as the lower part of the cervical region. The plantar reflex is obtained 

 by tickling the soles of the feet, when the leg on that side, or, it may be, both legs 

 are drawn up. It is always present in health, and its centre is in the lumbar 

 enlargement of the cord. The cremasteric reflex is well marked in boys, and is 

 easily produced by exciting the skin on the inner side of the thigh, when the 

 testicle on that side is retracted. The gluteal reflex consists in a contraction of 

 the gluteal muscles, when the skin over the buttock is stimulated. The abdominal 

 reflex consists in a similar contraction of the abdominal muscles, when the skin 

 over the abdomen in the mammary line is stimulated. The epigastric reflex is 

 obtained by stimulating the skin in front between the fourth and sixth ribs. The 

 interscapular reflex results in a contraction of the muscles attached to the scapula, 



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