LIFE. 29 
take no cognizance of an independent principle whose 
mysterious union with the body causes it to live, and 
whose separation leaves it to die. In the modern view, 
life is a system of functions, or the sum total of living 
phenomena. Many of these phenomena are evidently 
manifestations of the common force of nature, acting 
either mechanically, chemically, electrically, or osmotic- 
ally. 
Still, the combination of elements into organic cells, 
the arrangement of these cells into tissues, the grouping 
of these tissues into organs, and the marshaling of these 
organs into plans of structure, call for some further shap- 
ing, controlling power to effect such wonderful co-ordina- 
tion. Moreover, the manifestation of feeling and con- 
sciousness 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 labo- 
ratory." 
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 identical in all—a viscid, transpar- 
ent, homogeneous, minutely granular, albuminoid matter. 
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 vibra- 
tions. 
The essential manifestations of animal life may be re- 
duced to three: contractility, or the property possessed by 
certain parts of the body, especially the muscular fibres, of 
shortening themselves ; senszbzlity, or the peculiar power, 
confined to nervous matter, of receiving and transmitting 
impressions; and the power of assimilating food. All 
