CUTANEOUS AND MUSCLE REFLEXES AS DIAGNOSTIC SIGNS 527 



normal animal by impulses passing down from the cerebrum. Efferent 

 impulses produce dilatation of the vessels of the penis. 



The Parturition Center. The center for the expulsion of the contents of 

 the uterus in parturition is situated in the lumbar spinal cord rather higher 

 up than the other centers already enumerated. The stimulation of the 

 uterus may, under certain conditions, excite the center to send out impulses 

 which produce a contraction of the uterine walls and expulsion of the con- 

 tents of the cavity. The center is independent of the will since delivery 

 takes place in paraplegic women, and also while a patient is under the influ- 

 ence of chloroform. Again, as in the cases of defecation and micturition, the 

 abdominal and thoracic muscles assist; their action being for the most part 

 reflex and involuntary. 



Inhibition of Reflex Actions. Movements such as are produced by stimu- 

 lating the skin of the lower extremities in the human subject, after division 

 or disorganization of a part of the spinal cord, do not always occur when the 

 cerebrum is active and the connection between the cord and the brain is intact. 

 The reflex which would occur in the animal with spinal cord only is suppressed 

 or inhibited in the normal animal through the regulative action of the higher 

 cerebral centers. When one is anxiously thinking, even slight stimuli may 

 produce involuntary and reflex movements. So, also, during sleep, such reflex 

 movements may be observed, when the skin is touched or tickled; for example, 

 when one touches the palm of the hand of a sleeping child, the impression on 

 the skin of the palm producing a reflex movement of the muscles which 

 close the hand. But when the individual is awake no such reflex is produced. 



Further, many reflex actions are capable of being more or less controlled 

 or even altogether prevented by the will, of which the following may be quoted 

 as familiar examples: 



When the foot is tickled we can, by an effort of will, prevent the reflex 

 action of jerking it away. So, too, the involuntary closing of the eyes and 

 starting back, when a blow is aimed at the head, can be similarly restrained. 

 Darwin has mentioned an interesting example of the way in which such an 

 instinctive reflex act may override the strongest effort of the will. He placed 

 his face close against the glass of the cobra's cage in the Reptile House at 

 the Zoological Gardens, and, though of course thoroughly convinced of his 

 perfect security, could not by any effort of the will prevent himself from 

 starting back when the snake struck with fury at the glass. 



It can be readily shown, by comparing a spinal frog and a normal unin- 

 jured frog, that stimuli which call forth definite reflexes in the one often pro- 

 duce no movement of the other. 



Cutaneous and Muscle Reflexes as Diagnostic Signs. In the hu- 

 man subject two classes of reflex actions dependent upon the spinal cord are 

 usually distinguished, the alterations of which, either of increase or of diminu- 

 tion, are indications of some abnormality, and are used as a means of diag- 



