1885.] The Relations of Mind and Matter. 755 
the primitive system of direct and immediate communication be- 
tween the organs of sensation and the organs of motion. If in 
these forms intermediate ganglia exist, their sole duty may be 
that of a division of the current of energy and the drafting it off 
to the proper muscles, 
As we ascend to higher forms of animal life, however, a more 
developed sensitiveness appears. This is a necessary result of 
animal development. Higher life conditions require superior 
powers of perceiving prey or enemies, and greater quickness in 
pursuit or flight. For this, sensitiveness to more and more dis- 
tant impressions, to more delicate conditions of energy, and to a 
greater variety of emanations becomes requisite. The originally 
general sensitiveness must become specialized, and the nerves 
attain varied endings suitable to the reception of diversified modes 
of vibration or contact. 
This absolutely necessary consequence of the development of 
animal form yields another consequence of considerable import- 
ance. If the sensory organism becomes highly developed and 
capable of receiving delicate impressions both from near and far, 
the inflow of energy must become so great and continuous that 
a motor response to every sensation will become impossible. 
There must be some means of checking the inflowing current and 
preventing the whole of it from reaching the muscles, or the body 
will wear itself out from the very superiority of its organization. 
If the sensory currents be permitted to reach the muscle fibers 
these cannot but respond, and would thus be steadily in the con- 
dition of fatigue and incapability. It necessarily follows that a 
full development of nervous susceptibility is impossible unless in 
some method the excessively numerous external energies which 
beat upon the body can be prevented from bringing all their force 
to bear upon the muscles. 
This is the secondary phase in the development of the nervous 
function, and nature has chosen two methods of attaining the 
requisite end. In the one case, as the nervous substance grows 
more susceptible its sensitive terminations are covered by an in- 
durated material, through which energy cannot readily force its 
way. The special organs needed to receive the more delicate 
forms of energy are developed only on limited tracts of the body, 
and touch and temperature alone are capable of affecting the 
whole surface. With the great mass of animals the effects of* 
VOL, XIX.—NO. VIII. 50 
