LIFE. 
29 
collective name for the sum of the phenomena displayed 
by living beings. It is neither a force nor a thing at all, 
but is an abstraction, like goodness or sweetness; or, to 
use Huxley’s expression, to speak of vitality is as if one 
should speak of the horologity of a clock, meaning its 
time-keeping properties. 
A third theory is still possible. The combination of 
elements into organic cells, the arrangement of these cells 
into tissues, the grouping of these tissues into organs, and 
the marshalling of these organs into plans of structure, 
call for some further shaping, controlling power to effect 
such wonderful co-ordination. Moreover, the manifesta¬ 
tion of feeling and consciousness is a mystery which no 
physical hypothesis has cleared up. The simplest vital 
phenomenon has in it something over and above the known 
forces of the laboratory. 11 If the vital machine is given, 
it works by physical forces; but to produce it and keep 
it in order needs, so far as we now know, more than mere 
physical force. To this controlling power we may apply 
the name vitality . 
Life is exhibited only under certain conditions. One 
condition is the presence of a physical basis called proto- 
plasm . This substance is found in all living bodies, and, 
so far as we know, is similar in all—-a viscid, transpar¬ 
ent, homogeneous, or minutely granular, albuminoid mat¬ 
ter. Life is inseparable from this protoplasm; but it is 
dormant unless excited by some external stimulants, such 
as heat, light, electricity, food, water, and oxygen. Thus, 
a certain temperature is essential to growth and motion ; 
taste is induced by chemical action, and sight by luminous 
vibrations. 
The essential manifestations of animal life may be re¬ 
duced to four: contractility; irritability , or the peculiar 
power of receiving and transmitting impressions; the 
power of assimilating food; the power of reproduction . 
All these powers are possessed by protoplasm, and so by 
