INHIBITION OF REFLEXES. 731 



to 0.015 second. This time is increased by about a third if the impulse passes 

 to the opposite side or through the length of the cord (from the sensory root of 

 the anterior extremity to the motor root of the posterior extremity). Heat 

 diminishes the reflex time and increases the 'reflex activity. Lowering of the 

 temperature (winter- frogs) , likewise the poisons previously mentioned that in- 

 crease reflex activity, increase the reflex time, while at the same time increasing 

 reflex irritability. Conversely, the reflex time diminishes with increase in the 

 intensity of the stimulus and it may thus even be of minimal duration. It would 

 appear as if the reflex resulting from the action of a strong stimulus tra- 

 verses a shorter path (spinal cord in the frog) than that resulting from the action 

 of a feeble stimulus, in which case the impulse must ascend to the portion of the 

 cord below the calamus scriptorius, where the transfer takes place. There are, 

 thus, two reflex paths, one for strong stimuli, the other for feeble stimuli, the 

 latter being generally the normal. 



The reflex time can be measured by noting the time of irritation of the sensory 

 fiber and that of contraction. From the result thus obtained there must be 

 deducted the time required for conduction through the two nerve-tracts, as well 

 as the duration of the latent stimulation. 



In accordance with their location Jendrassik divides the reflexes as follows: 



I. Spinal reflexes (tendinous, muscular, periosteal, bony, articular, genital- 

 muscle reflexes. The pathological spinal reflex occurs only in case of total or almost 

 total transverse section of the spinal cord and is manifested as flexor, less com- 

 monly as extensor, movement of the lower extremities. 



II. Cerebral cortical reflexes, elicitable especially by tickling the skin: scapular, 

 abdominal, cremasteric, scrotal, gluteal, plantar, auricular, palpebral, palatal, con- 

 junctival, anal reflexes. 



III. Complex reflexes, for which a spinal and a cerebral reflex center are 

 necessary: sneezing, vomiting, swallowing, coughing, evacuation of bladder and 

 rectum, ejaculation, all of which belong to the vegetative functions. 



INHIBITION OF REFLEXES. 



There exist in the body mechanisms, by means of which the pro- 

 duction of reflexes can be suppressed, and which accordingly have been 

 designated reflex-inhibiting mechanisms : 



1 . Through the action of the will reflexes both in the cerebral and in 

 the spinal distribution can be voluntarily inhibited; for example, keeping 

 the eyes open when the bulb is touched ; suppression of movement on tick- 

 ling the skin. It should, however, be observed in this connection that the 

 inhibition of the reflexes is possible only to a certain point. If the stimu- 

 lus be strong and frequently repeated the reflex action finally predomi- 

 nates over the volitional inhibitory impulses. Moreover, such reflex 

 movements as cannot under any circumstances be executed voluntarily, 

 cannot be inhibited. Thus, erection, ejaculation, the act of parturition, 

 and the movements of the iris can neither be executed voluntarily, 

 nor if excited reflexly can they be inhibited by the will. 



2. Setschenow' s inhibitory center is the designation given to another 

 cerebral apparatus, located in the frog on both sides in the optic thalamus 

 and the quadrigeminate bodies. Separation of these parts by section 

 increases reflex irritability, while irritation of the lower cut surface (by 

 sodium chlorid or blood) suppresses reflex movements. This result can 

 be observed also on one side. It is believed that analogous organs exist 

 in the higher vertebrates in the quadrigeminate bodies and in the medulla 

 oblongata. From what has been said, it is clear,that reflexes occur more 

 regularly and are more readily elicited after exclusion of the brain. 



3. Strong irritation of a sensory nerve suppresses reflex movement. 

 The reflex does not appear even when the centripetal nerve involved is 

 strongly irritated; for example, inhibition of sneezing by friction of the 



