June 5, 1908] 



SCIENCE 



887 



2.3 per second; and some reflexes consist of a 

 single indivisible discharge. The rhythm of 

 reflex discharge may be conceived as de- 

 pendent on a " refractory phase " somewhere 

 in the arc, similar in a broad vray to the re- 

 fractory phase of the heart. Whereas the re- 

 fractory phase of a nerve trunk is not longer 

 than .001 second, that of reflex discharge, 

 varying in different reflexes, sometimes 

 reaches as high as a second. The author has 

 studied in a penetrating way the question of 

 the seat of the refractory phase in the reflex 

 arc. He shows that it can not lie in the 

 muscle or motor neurone, nor in the sense 

 organ or sensory neurone. It must lie in the 

 central distributing and coordinating neu- 

 rones, each of which has a refractory phase 

 adapted in duration to the particular use of 

 its reflex. Dependent on the central neurones 

 is also the inhibition of muscular activity op- 

 posed to the reflex. As compared with the 

 nerve trunk, the reflex arc is also much more 

 susceptible to fatigue, shock, deprivation of 

 oxygen, and the action of anesthetics. It is 

 interesting to observe that the author inclines 

 to attribute all these peculiarities to the 

 synapse or surface of separation between con- 

 necting neurones, and that he is favorable to 

 their explanation by the physical properties of 

 such a surface of separation, with its well- 

 known power to produce partial, selective and 

 polarized osmosis, and to restrict the move- 

 ment of ions. 



Passing from the simple reflex to the com- 

 bination and coordination of reflexes, the 

 author emphasizes first of all the principle of 

 the " common patL" Eeflex arcs which start 

 at different parts of the skin or other sense 

 organs may converge so as to act on the same 

 muscle or group of muscles. Thus, for ex- 

 ample, the flexors of the joints of the hind 

 limb can be aroused by stimulating almost 

 any point on the skin of that limb, as well as 

 from certain other parts of the surface and 

 interior of the body. More than this, the 

 same muscles are called into play in other re- 

 flexes, such as the scratching or the stepping 

 reflexes, in which the time relations difier 

 from those seen in the flexion reflex. It ap- 



pears that the muscles, and with them the 

 motor neurones which directly control them, 

 can be aroused from various sources, and in 

 ways that differ to a greater or less extent. 

 The motor neurone, extending from the cord 

 to the muscles, is therefore a common path, 

 forming part of many reflex arcs. This fact 

 is important in understanding coordination. 

 There are reflexes which use the same muscles 

 in the same way; they may be called allied 

 reflexes. As they can make simultaneous use 

 of the same muscles without interfering in 

 any way with each other, they tend to rein- 

 force each other. But there are reflexes which 

 make use of a given set of muscles in ways 

 that are incompatible with each other; one 

 may require the inhibition of activity where 

 the other requires the activity, or they both 

 require activity, but in differing intensity or 

 duration or rhythm. Such opposed reflexes 

 could not, and do not, have simultaneous use 

 of the same muscles. When the final path is 

 open to one of them, it is closed to the other. 

 And it is closed absolutely. If the stimuli 

 appropriate to two antagonistic reflexes are 

 simultaneously applied, one or the other ap- 

 pears, but never a compromise or average of 

 the two, which would indeed be a useless reac- 

 tion. If during the progress of one reflex the 

 stimulus to another is applied, it may cause a 

 cessation of the first and its replacement by 

 the second, but the transition is abrupt; the 

 first does not shade off into the second. If a 

 stimulus, at first weak and arousing a local 

 reflex, is gradually increased in intensity, the 

 reflex tends to spread to other muscles and 

 other members, but all the components so 

 added to the original focal reflex are allied. 

 The total reflex pattern at any moment — ex- 

 cept for reflexes neutral to each other and 

 without influence on each other, which may 

 coexist to a very limited extent — may thus be 

 analyzed into a combination of allied simple 

 reflexes. 



In the succession of reflexes quite a different 

 principle comes into play, for it is commonly 

 true that a reflex is followed by an antago- 

 nistic reflex. One frequent form of sequence 

 is the return after a reflex to the posture 



