18 



PROTOPLASM AND THE CELL 



a temperature of about 30 C. and decreases with lessening temperatures 

 down to the freezing-point of water. When C. is nearly reached, 

 movements apparently cease altogether, although vital molecular move- 

 ments doubtless continue. Certain forms of life, especially some spores 

 and many kinds of bacteria, endure even the cold of liquid air and that 

 of other still colder solidified gases, reviving uninjured when allowed to 

 become warm again. 



Such are some of the more important external characteristics of the 

 physical basis of life, that is, of the quasi-undifferentiated protoplasm 

 which composes many of the infusoria, etc. Differentiated protoplasm, 

 comprising the tissues of animals of more complex structure, has many 

 other colors, specific gravities, consistencies, and physical qualities, 

 many of which are described by the science of histology. 



FIG. 1 



Food vacuole 



Nucleus. 



VojClLolti 



Pulsating 

 uacuole 



e^nmm 

 ,ISiti } 



Ameba proteus. The nucleus, cytoplasm, metaplasm, " endoplasm," " ectoplasm," contractile 

 vacuoles, food-vacuoles, other vacuoles, new and old, are easily made out. Oftentimes, besides, 

 these formless masses of food debris are to be seen colored green, yellow, or red. X 60. 



Hypotheses as to the Origin of Life. About the origin of life, especially 

 on this planet, there has always been much speculation, and we may well 

 mention the four or five leading hypotheses, only one of which, however 

 the last tends slowly to some degree of present confirmation: (1) One 

 theory of the source of terrestial life may be read in the first chapter of 

 Genesis. It is obvious that such an allegorical account of the matter, 

 however picturesque, has little scientific interest in the light of evolu- 

 tionary philosophy, for the account fails to state how the creation was 

 performed, which in itself is the problem. (2) The theory of hylozoism, 

 that the world itself is inherently alive and that the inorganic is conse- 

 quently secondary to the organic, has much philosophical interest, but 

 little present proof or importance as a scientific theory. (3) H. E. 

 Richter, Lord Kelvin, and even the great Helmholtz, discussed the 

 proposition that life is eternal and that its germs came to earth in meteors 

 or in other ways from other planetary specks in the universe. This 



