SCIENCE 



[N. S. Vol. XXVII. No. 701 



present before the reflex. This posture was 

 itself reflex, and the return to it is by no 

 means a passive movement, but is an active 

 compensatory reaction. Very frequent in the 

 spinal as well as in the intact animal are 

 alternating reflexes, as stepping, scratching, 

 etc. One of the most important original con- 

 tributions of the author is the discovery of 

 " successive spinal induction." A reflex which 

 has been just preceded by an antagonistic re- 

 flex is found to be more readily excited than 

 usual and to have greater energy. Inhibition 

 of a reflex is " followed by a rebound to super- 

 activity." As is the case in the heart muscle, 

 so also in the spinal cord, the period of inhibi- 

 tion is not simply equivalent to a period of 

 rest, but the activity of a reflex after active 

 inhibition is greater than after repose. This 

 fact has much to do with the orderly and 

 adaptive sequence of an animal's movements. 



Since it seldom happens that an animal is 

 subjected to only one stimulus at a time, there 

 is usually a competition between stimuli for 

 control of the common paths. Prominent 

 among the factors which make for success in 

 this competition is intensity, the more intense 

 stimulus having the advantage. But the in- 

 tensity of the physical stimulus must be con- 

 sidered in connection with its location, for 

 within the " receptive field " of a reflex, the 

 more central portions give the reaction with 

 weaker stimulation than do the more periph- 

 eral. Account must also be taken of other 

 simultaneous or immediately preceding 

 stimuli, since simultaneous stimuli that 

 tend to arouse the same reflex, or preced- 

 ing stimuli that have inhibited it, favor its 

 appearance. The relative fatigue of different 

 reflexes also influences the result of the com- 

 petition. And, finally, the different species of 

 reflexes are elicited with unequal ease. At 

 the bottom of the scale stand the tonic re- 

 flexes, which very readily yield to others ; and 

 at the top, easiest to arouse, stand the reac- 

 tions to injurious ("painful") stimuli, or to 

 other stimuli which, considered from the point 

 of view of sensation, have a strong affective 

 tone. 



In the chapters devoted to the brain, we 



find, besides the author's revision of the motor 

 area, which is by now familiar, the observa- 

 tion that cortically originating movements 

 are related in the same ways as spinal re- 

 flexes, being mutually allied, antagonistic or 

 neutral. From the cortex, as in reflex excita- 

 tion, the same stimulus which arouses a move- 

 ment inhibits the opposing muscles. Also, the 

 species of movements which can most easily 

 be aroused by reflex paths can likewise be 

 most easily aroused from the cortex, while 

 such as can not be easily aroused reflexly are 

 also very difiicult of access by cortical stim- 

 ulation. Flexions are in general easily 

 aroused, extensions with diflSculty. This does 

 not mean that the " cortex is in touch with the 

 flexors alone and not with the extensors. It 

 means that the usual effect of the cortex on 

 these latter is inhibition." The muscles of 

 the body are not all on a par as regards reac- 

 tion to stimuli, but may be broadly grouped 

 into two systems, a tonic system, in which the 

 extensors of the limbs are prominent, and a 

 phasic system, in which the flexors are promi- 

 nent. The muscles of the tonic system are 

 usually kept in a condition of feeble tonic 

 contraction, by means of which the posture of 

 the animal is maintained. The phasic system 

 responds to intercurrent stimuli; the posture 

 is abandoned, inhibited, and a brief reaction, 

 the first step in which is usually flexion, oc- 

 curs, after which a compensatory movement 

 brings back the previous posture. The stimuli 

 which bring about tonus originate largely in 

 the interior of the limbs and in the otic 

 labyrinth. This system of sense organs is 

 excited by mechanical means, especially by 

 movements and tensions resulting from the 

 contractions of the muscles and the move- 

 ments and positions of the body. The chief 

 center of this system, or, as we may call it in 

 terms derived from the segmental conception 

 of the nervous system, the ganglion of the 

 system, is in the neighborhood of the principal 

 sense organ belonging to it; this ganglion is 

 the cerebellum. The cerebrum, similarly, may 

 be considered as the ganglion of the great 

 sense organs of the head, which have as their 

 peculiar function the receiving of stimuli 



