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 three: contractility ; sensibility, or the peculiar 

 power of receiving and transmitting impressions ; and the 

 power of assimilating food. All these powers are pos- 



