740 REPORT—1904. 
show high contemporaneous activity (strychnia, some forms of ‘willed’ action). 
I think, rather, that in some way the terminal of that are which for the moment 
dominates the final common path, disconnects that path from all terminals dissi- 
milar from itself. 
Whatever be the nature of the physiological process in the conflict between 
the competing reflexes, the issue of that conflict—namely, the determination 
of which competing are shall for the time being reign over the final common path— 
is largely conditioned by three factors. One of these is the relative intensity of 
the stimulation of the rival reflexes. An arc strongly stimulated is ceteris 
paribus more likely to capture the common path than one which is excited feebly. 
In the spinal dog, retraction equally induced in both legs mutually excludes the 
crossed extension of either side, but if unequally induced allows the crossed exten- 
sion of the stronger reflex to exclude the weaker reflex altogether. The common 
path is probably never out of the grasp of some one or other reflex. Thus, in the 
spinal dog even, with its limb apparently at rest, this is true. The final common 
path of the extensor of the knee lies, then, in the hands of a tonic reflex arising 
in the muscle itself. Given a strong skin stimulus, and it passes under the mastery 
of the reflex arising in the stimulated skin; but when that is over, the tonus are 
immediately repossesses it, and for a short time, as shown by the knee-jerk, more 
strongly than before. 
A second main determinant for the issue of the conflict between the rival 
reflexes is the functional species of those reflexes. Arcs belonging to species 
of receptors which, considered as sense-organs, provoke strongly affective sensation 
—e.g. pain, sexual feeling, &c—win the final common path with remarkable 
facility. Such reflexes override and set aside with peculiar potency reflexes 
belonging to touch organs, muscular sense-organs, &c. As the sensations evoked 
by these arcs—e,g. pains—exclude and dominate concurrent sensations in con- 
sciousness, so do the reflexes of these arcs prevail in the competition for posses- 
sion of the common paths. They seem capable of pre-eminent intensity of action. 
A third main factor deciding the conflict between the competing reflexes is 
‘fatigue.’ An are under long continuous stimulation of its receptor tends, even 
when it holds the common path, to retain its hold less well. Other arcs can then 
more readily dispossess it. A stimulus to a fresh arc has, in virtue of its mere 
freshness, a better chance of capturing the common path, The common path does 
not tire. In the scratch reflex under stimulation of sa, when the motor discharge 
becomes slow and irregular from fatigue, it is still perfect for 88, or L, &c. 
(Fig. 1, B). This waning of a reflex under long-maintained excitation is one of 
the many phenomena that pass in physiology under the name ‘fatigue.’ Its 
place of incidence lies at the synapse. It seems a process elaborated and pre- 
served in the selective evolution of the neural machinery. It prevents long con- 
tinuous possession of a common path by any one reflex of considerable intensity. 
It favours the receptors taking turn akout. It helps to ensure serial variety of 
reaction. The organism, to be successful in a million-sided environment, must in 
its reactions be many-sided. Were it not for such so-called ‘ fatigue,’ an organism 
might, in regard to its receptivity, develop an eye, or an ear, ora mouth, or a 
hand or leg, but it would hardly develop the marvellous congeries of all those 
various sense-organs which it actually does. 
But while talking of fatigue in general I forget the fatigue in particular of 
listeners. The principle I have tried to outline to you has many and wide appli- 
cations ; it seems fruitful for problems of Pathology and Psychology, as well as for 
those of Physiology. But I keep you too long. Let me sum up. The reflex arcs 
(of the synaptic system) converge in their course so as to impinge upon links 
possessed by whole varied groups in common—common paths. This arrangement 
culminates in the convergence of many separately arising arcs upon the efferent- 
root neurone. This neurone thus forms a final common path for many different 
reflex arcs and acts. It is responsive in various rhythm and intensity, and is 
relatively unfatigable. Of the different arcs which use it in common, each can 
do so exclusively in due succession, but different arcs cannot use it simultaneously, 
There is, therefore, interference between the actions of the arcs possessing the 
