830 THE SPINAL CORD. 



tion is dependent on the strength of the stimulus, being proportional to it at 

 the beginning of the period and becoming gradually less so as the period 

 advances. But the reflex responses referred to in these observations under 

 strychnin are of the nature of general convulsions, and the liminal intensity 

 of stimulus under strychnin is high. 



The direction of the reflex movement is sometimes with intense stimuli 

 the reverse of that evoked by weak stimuli. In the spinal eel a light touch 

 on the side of the body causes that side to be approached toward the 

 stimulus ; an intense stimulus, e.g. hot iron, causes it to be withdrawn from the 

 stimulus (Pfliiger). The eel's touch reflexes exhibit " positive stereotropism " 

 (Loeb), the pain reflexes "negative stereotropism." 



The character of the muscular response. — The reflex contraction 

 of a skeletal muscle may be almost as brief as the simple twitch due 

 to momentary stimulation of the motor nerve, 1 or it may be as pro- 

 longed as a long tetanic contraction. It has been suggested that 

 every reflex contraction is tetanic in nature 2 ; but this remains unproven, 

 and is by some denied. 3 Only in rare instances is a single muscle 

 alone thrown into contraction if the contraction be vigorous. On 

 the other hand, if the reflex be very weak, it often consists in a 

 slight flickering in a single part of a single muscle ; one can note 

 this well in the gracilis muscle of the spinal mammal. The dura- 

 tion of the reflex contraction, unlike that of the contraction evoked by 

 stimulation of the motor nerve, tends to continue after cessation of 

 a brief stimulus and to fail before cessation of a prolonged stimulus. 4 

 The reflex spinal movement, if prolonged, tends always, in my ex- 

 perience, to be of alternating character, offering in this respect a 

 striking difference from a movement of similar duration evoked from 

 the cortex. A movement from the initial posture of rest to another 

 posture is obtained ; this is the primary movement, and with it the 

 reflex reaction, if of short duration, may come to an end. But 

 with prolongation of the reflex action, the posture first attained is not 

 maintained. A second movement, opposed in sense to the former, sets 

 in. And this alternation of postures may be repeated a number of 

 times. Examples are the wagging movement of the tail, and the 

 repeated " kicks " of the spinal cat when one hind-paw is held. The 

 rhythmic alternation is still more frequent in the " scratching " 

 reflex, where a scrabbing movement of the ankle and foot occurs 

 with alternations of 3 to 5 per second. Also in the " shaking " 

 reflexes, where the animal shakes its ears or its body, as does a dog 

 on coming out of water. In their phasic alternation of condition 

 the motor cells pass through periods of discharge and quiescence ; 

 the contraction and the relaxation contemporaneously affect antagon- 

 istic muscles, and successively affect synergic muscles. Through- 

 out the phases of this sequence, in which inhibition as well as 

 excitation seems to play a part, it is only harmoniously acting 

 regions of musculature that are at one and the same time in con- 

 traction. Thus in the rectus femoris muscle the part that flexes 

 the hip contracts alternately with the part that extends the knee, 

 and, on the other hand, synchronously with the other hip flexors 



1 Wundt, 0]). cit. W.'s observations were made under weak strychnisation ; Stirling 

 and Kronecker employed unpoisoned preparations. 



2 Stirling, with Kronecker, loc. cit. 



3 Wundt, "Untersuch. z. Mechanik. d. Nervencent," 1876, Bd. i. Abth. 2. 



4 Beaunis, "Rech. expeY sur les condit. de l'activite cdrebrale," Paris, 1884, p. 106. 



