Literary Notices. 203 



The simple reflex is an abstraction for in reality no reflex exists independently; 

 there is always coordination. This coordination is of two sorts; simultaneous and 

 successive; the former gives origin to the reflex-patterns, the latter to the chain- 

 reflexes or shifting patterns by which the parts of the body are constantly brought 

 into adaptive relation to one another and to the changing environment. 



Briefly and pointedly the author discusses the role of each of the elements of the 

 reflex-arc. The chief function of the receptor is selective excitability; "it lowers 

 the threshold of excitability of the arc for one kind of stimulus, and heightens it 

 for all others" (p. 12). Point by point the characters of nerve-arc conduction are 

 exhibited in the Hght of the reflexes of the spinal dog. Nerve-arc conduction differs 

 from nerve-trunk conduction in eleven important respects: latent period, after- 

 discharge, relation of rhythm of end-effect to rhythm of stimulus, relation of inten- 

 sity of stimulus to end-effect, summation, irreversibility of direction of impulse, 

 fatigability, variability of the threshold, refractory period, dependence on blood-cir- 

 culation, susceptibility to drugs (p. 14). The first three lectures present the results 

 of intensive research concerning each of these eleven features of nerve-arc conduc- 

 tion, together with interpretations of the results in terms of adaptive reactions. 



Many of the differences between the conduction of the reflex-arc and the nerve 

 trunk Sherrington thinks are to be referred to the inter-neurone region, the 

 synapse. Irreversibility of the direction of conduction is due, possibly, to the fact 

 that the synaptic membrane is more permeable in one direction than in the other 

 (p. 42). 



In the discussion of refractory phase, we have an excellent illustration of the way 

 in which the author gives life to his book by pointing out the significance of his 

 facts. "The scratching-reflex, in order to secure its aim, must evidently consist of 

 a succession of movements repeated in the same direction, and intervening between 

 the several numbers of that series there must be a complemental series of movements 

 in the opposite direction. Whether these two series involve reflex contractions of 

 two antagonistic muscle-groups, respectively, in alternate time, I would leave for the 

 present. The muscle groups or their reflex-arcs must show phases of refractory 

 state during which stimuli can not excite, alternating with phases in which such 

 stimuli easily excite. Evidently this is fundamental for securing return to the 

 initial position whence the next stroke shall start. The refractory phase secures 

 this. By its extension through the whole series of arcs it prevents that confusion 

 which would result were refractory phase in some of the arcs allowed to concur with 

 excitatory phase in others" (p. 63). And further, in the same connection, to show 

 the value of inhibition and the reasons for the existence of central as well as peri- 

 pheral inhibition, he states that the scratch-reflex "is but one of several reflexes 

 that share in a condominium over the effector organ — the limb. It must, there- 

 fore, be possible for the scratch-reflex taken as a whole, to be, as occasion demands, 

 replaced in exerciseof its use of the limb by other reflexes, and many of these do not 

 require clonic action from the limb — indeed, would be defeated by clonic action. It 

 would not do, then, for the peripheral organ itself to be a clonic mechanism. The 

 clonic mechanism must lie at some place where other kinds of reflex can preclude 

 the clonic actuator from affecting the peripheral organ. Now such a place is 

 obviously the central organ itself; for that organ is, as its name implies, a nodal 

 point of meeting to which converge all the nervous arcs of the body, and among others 

 all those which for their several ends have to employ the same mechanical organ as 



