THE PHENOMENA OF LIFE. 3 



are justified in describing it, with Huxley, as the " physical basis of 

 life," or simply " living matter/' 



A cell may now be defined as a nucleated mass of protoplasm, of 

 microscopic size, varying in the human body from the red blood-cell 

 which is about ^Vg- of an inch in diameter to the ganglion -cell, ^ of 

 an inch, which possesses sufficient individuality to have a life-history of 

 its own. Each cell originates from a pre-existing cell, grows, produces 

 other cells, and dies, going through the same, though briefer, cycle as the 

 whole organism. Some of the lower forms of life seem to consist of non- 

 nucleated protoplasm, but the above definition holds good for all the 

 higher plants and animals, though some few celis lose their nuclei in 

 the course of development, e.g., the red blood-cells of all mammals. 



Properties of Protoplasm. 



Protoplasm is a semi-fluid substance, which swells up but does not 

 mix with water. It is transparent and generally colorless, with refrac- 

 tive index higher than that of water but lower than that of oil. It is 

 neutral or weakly alkaline in reaction, but may under special circum- 

 stances be acid, as, for example, after activity. It undergoes stiffening 

 or coagulation at a temperature of about 54.5 C. (130 F.), and hence 

 no organism can live when its own temperature is raised above that 

 point ; it is also coagulated and therefore killed by alcohol, by solutions 

 of many of the metallic salts, by strong acids and alkalies, and by many 

 other substances. 



Under the microscope it is seen almost universally to be granular, the 

 granules consisting of different substances, either albuminous, or fatty, or 

 glycogenous matters, or more rarely of inorganic salts. The granules are 

 not equally distributed throughout the whole cell-mass, as they are some- 

 times absent from the outer part or layer, and very numerous in the 

 interior. The granules may exhibit an irregular shaking, dancing move- 

 ment, which is not vital and is known as the Broivnian movement. In 

 addition to granules, protoplasm generally exhibits spaces or vacuoles, 

 generally globular in shape, excepting during movement when they may 

 be irregular, filled with a watery fluid. These vacuoles are more numer- 

 ous and pronounced in vegetable than in animal cells. Gas bubbles also 

 sometimes exist in cells. 



It is impossible to make any definite statement as to the exact chem- 

 ical composition of living protoplasm, since the methods of chemical 

 analysis necessarily imply the death of the cell; it is, however, stated 

 that protoplasm contains 75 to 85 per cent of water, and of the 15 to 25 

 per cent of solids, the most important part belongs to the classes of sub- 

 stances called proteids or albumins. Proteids contain the chemical ele- 

 ments carbon, hydrogen, nitrogen, oxygen, sulphur, and phosphorus, the 



