500 F. H. PIKE 
hypothesis is. For any compensatory increase in the activity 
of the lower neurones must be subtracted from the supposed 
shock effect, and a corresponding amount must be added to 
the supposed function of the cerebral cortex, as determined by 
the criterion of a minimal deficiency of function. Asthe problem 
stands at present, there are three unknown quantities: 1) the 
exact function of the lower neurones, motor, sensory, com- 
missural or association; 2) the amount of change of a progressive 
nature rather than retrogressive, which the lower motor neurones 
undergo after separation from the higher, and, 3) the exact 
function of the higher neurones. None of the quantities has 
been measured independently and directly, and the number of 
equations so far proposed is less than the number of unknown 
quantities. It seems idle, therefore, to introduce a fourth 
unknown quantity—the shock effect—or even a fifth, such as 
vicarious assumption of function, and to ascribe arbitrary limits 
to it, when the determination of its real value must await either 
a demonstration of its actual extent and potency or the solu- 
tion of the equations involving the three other unknowns. 
Certain considerations other than those already adduced may 
be brought forward in connection with the discussion of von 
Monakow’s views. Diaschisis, or shock, or whatever other 
name one may apply to the change which occurs in the lower 
levels of the central nervous system when they are separated 
from the higher, isa reversible change. I have already referred 
to Sherrington’s statement that, when the shock effect has once 
been induced in the spinal cord by anatomical transection, a 
second transection below the first has no further effect. In this 
case the anatomical separation of one portion of the central 
nervous system once for all from the remaining portions would 
preclude any reciprocal action of one part upon the other. No 
possibility of a reversible reaction dependent upon a connection 
of the lower levels with the higher exists under such conditions. 
But when the function of the higher levels of the central nervous 
system is temporarily abolished, by tying off the arteries to the 
head, the lower part exhibits at first signs of shock similar to 
those seen after anatomical transection. There is, however, a 
