600 THE FUNCTION OF THE SPINAL CORD 



regarded as a pseudo or axone reflex, i.e., as one which is had without 

 the intervention of the cell-body or center. In other words, the im- 

 pulse set up in the receptor, passes no farther than the next collateral, 

 where it finds a direct course to the effector. This explanation, 

 as has just been stated, was intended to bring the extremely brief time 

 of the patellar reflex into relation with the speed of the nerve impulse, 

 as determined by the older methods. Applegarth, for example, has 

 stated that the patellar reflex time is 0.014-0.02 sec. (dog), while 

 Waller and Gotch found it to be 0.008-0.005 sec. (rabbit). Later on, 

 however, it has been shown by means of the string galvanometer, 

 that the speed of the nerve impulse in warm-blooded animals may 

 amount to more than 100 m. in a second. In addition, Snyder^ and 

 Hoffmann^ have ascertained that the patellar reflex time lies somewhere 

 between 0.0113 and 0.024 sec. These figures, therefore, prove very 

 conclusively that the patellar reflex must involve the spinal center; 

 at least, the time allowed for it is sufficient to complete the entire 

 circuit from the ligament to the cord and back again to the muscle. 



The objection has also been raised that the contraction of the 

 muse, quadriceps is a simple twitch and not a tetanus, as is usually 

 the case when muscles are activated reflexly. Much has also been 

 made of the fact that the aforesaid muscle reacts best when subjected 

 to a slight tension. It has been found, however, that not all muscular 

 responses are tetanic in their character. Sherrington,^ for example, 

 has called attention to the fact that the so-called ''extensor thrust" 

 which may be obtained in animals by suddenly pressing upon the 

 plantar surface of the hind foot, consists of simple contractions of the 

 extensor muscles of the hind leg. Lastly, it has been proved that 

 any injury to the lumbar segment of the spinal cord destroys the 

 patellar reflex and that its abolition may also be effected by dividing 

 either the posterior or the anterior roots of the cord. Obviously, 

 therefore, the production of the patellar reflex necessitates not only 

 an intact spinal center but also intact centripetal and centrifugal 

 paths. Its reflex nature, therefore, seems to be thoroughly established. 

 A similar controversy has led to the establishment of the fact that the 

 Achillis jerk is a true reflex. 



Reinforcement of Reflexes.^ — In testing the different reflexes, it 

 soon becomes apparent that the subject must remain in a state of perfect 

 inattention, otherwise the response will be less intense, or may, in 

 fact, be entirely abolished. In other words, if the attention of the 

 subject is directed to the procedure of eliciting the reflex, the usual 

 result is its inhibition by the cerebral centers. In this way, a diagnosis 

 of abolition of reflexes may be made which in reality is nothing more 

 than a normal phenomenon. This diflftculty may be easily overcome 



1 Am. Jour, of Physiol., xxvi, 1910, 474. 



2 Archiv fiir Physiol., 1910, 223. 



3 Jour, of Physiol., xxxviii, 1909, 375. 



^ First observed by Jendrassik in 1883. 



