INHIBITION OF REFLEXES. 733 



the cells of the gray matter must be diminished. The latter may be brought 

 about by the action of the poisons mentioned, as well as under the influence of 

 general increase in nervous irritability, such as is observed in cases of hysteria 

 and neurasthenia. Thus, extensive reflex convulsions may occur as a result of 

 increase in the intensity of the stimulus or of a diminution in the conduction- 

 resistance in the spinal cord. Of those measures that have been shown by experi- 

 ence to diminish or prevent reflex manifestations, the conclusion is justified that 

 they interpose increased resistance in the conducting paths of the reflex arc. The 

 action of influences inhibiting reflexes must) be interpreted in a similar manner. 

 As, obviously, the fibers of the reflex arc must be connected with the reflex-in- 

 hibiting conducting tracts, it is believed that, through the reflex-inhibiting stimu- 

 lation, resistance is at the same time interposed in the reflex arc. Difficulty is 

 encountered in explaining the widespread, coordinated reflexes according to the 

 view discussed. It has been assumed that from long use and also through hereditv 

 those groups of ganglion-cells that first receive the impulses are placed in com- 

 munication, under conditions most favorable to conduction, with others that trans- 

 mit the impulse to those groups of muscles whose activity best removes the body 

 or the respective member from possible injurious effects of the stimulus by a 

 coordinated, purposive movement. Thus, a stimulus always excites a group of 

 ganglion-cells coordinated by practice and responding to the stimulus as an har- 

 monious, coordinated motor mechanism. 



Pathological. Abnormalities in the reflex activity afford the physician a 

 large and important field in the investigation of diseases of the nervous system. 

 Enfeeblement or even abolition -of reflex activity may occur (i) as a result of 

 impairment or loss of irritability in the centripetal fibers; (2) as a result of analo- 

 gous disorders in the central organs; (3) or, finally, in the centrifugal fibers. The 

 reflexes are enfeebled or abolished when the entire nervous system is greatly 

 depressed, as after concussion, compression, inflammation of the central organs, 

 during asphyxia and deep coma, and in consequence of various intoxications. 

 After division of the upper portion of the spinal cord in man, and in apes, abolition 

 of the reflexes is often observed in the parts below the level of division. It 

 appears that the upper portions of the cord contain the region where normally 

 the reflexes are readily transferred, and after division of which the reflexes are in 

 abeyance. Dogs and cats, like the frog, exhibit active reflexes after division of 

 the spinal cord. 



Under abnormal conditions special attention has been given to the behavior 

 of certain reflexes, for example the so-called tendon-reflexes, which consist in 

 reflex contraction of a muscle when a blow is struck on its tendon, for example 

 the quadriceps extensor of the thigh, the tendo Achillis. etc. Thus, Westphal, 

 Erb. and others have found that the tendon-reflexes, particularly the patellar- 

 tendon reflex, also known as knee-phenomenon or knee-jerk, is almost constantly 

 wanting in cases of ataxic tabes dorsalis, but is abnormally increased and extensive 

 in cases of spastic spinal paralysis, which is characterized^ by a lesion of the pyra- 

 midal tracts. Division of the muscle-nerves abolishes the patellar phenomenon 

 in rabbits, as does also division of the spinal cord between the fifth and sixth 

 lumbar vertebra 1 . In Landois the contraction of the quadriceps occurred 0.040 

 second after the blow upon the patellar ligament; according to Jendrassik 0.039 

 second after the blow. A stronger blow has no effect upon the reflex time. Ac- 

 cording to Westphal these phenomena are not simple reflex processes, but com- 

 plicated phenomena related to muscle-tone, so that, for example, diminution in 

 the tone of the quadriceps fcmoris may abolish the phenomenon. The intact 

 existence of the external segments of the posterior columns of the spinal cord 

 is necessary for the preservation of the phenomenon. It is enfeebled by ph; 

 or mental fatigue and increased by transitory stimuli that involve the attention. 

 Jendrassik found it especially marked when muscles of the body were contracted 

 voluntarily, for example the muscles of the arm. It is enfeebled by strong and 

 prolonged contraction and extreme tension. 



Another reflex of diagnostic importance is the abdominal reflex, which consists 

 in contraction of the abdominal muscles on stroking the skin of the abdomen with 

 the handle of a percussion-hammer. Thus absence of this reflex on both sides is 

 indicative of diffuse disease of the brain in the presence of a cerebral disorder. 

 Absence on one side is indicative of a local disorder in the opposite half of the cere- 

 brum. The hypochondriac, anal, cremasteric, conjunctival. mammillary, pupil- 

 lary, nasal reflexes and others may also be made objects of investigation. Cerebral 

 lesions attended with hemiplegia always exhibit diminution of the reflexes upon 



