8 THE SMALLEST LIVING THINGS 



bacteria, like the largest, come from pre-existing organisms simi- 

 lar to themselves. If, as is generally believed, the concept ex- 

 pressed by the above aphorism, and upon which the entire science 

 of heredity is based, is universally true, then it follows that all 

 living things today represent protoplasm that has been con- 

 tinuously living since life commenced, and that the protoplasm of 

 a minute ameba, visible only with the microscope, is just as old 

 as the protoplasm of man. 



Lower and Higher Organisms 



If protoplasm was originally formed under special physical 

 and chemical conditions, as conceived by Huxley, then it is pos- 

 sible that the protoplasms thus formed were not equally potent. 

 Some types of that primordial protoplasm may have possessed in 

 high degree what Osborn calls the "potential of evolution" — the 

 capacity to develop into higher forms — while other types may 

 have had this potential in lesser degree. In the long history of 

 the earth the latter {e.g., Protozoa which have persisted through- 

 out) never advanced to high grades of specialization, whereas the 

 former, because of their greater capacity for change, evolved 

 into the complicated forms of animal and plant life found today. 

 There is no reason to believe that "higher" animals have evolved 

 from the forms that exist today as "lower" animals, but there 

 is a possibility that all animals, "higher" or "lower" in organi- 

 zation, may have had a common but unequally potent type of 

 ancestral protoplasm back in the protoplasm-forming age. 



There is some logical basis for the popular conception of 

 higher and lower types of organisms. When so used, however, 

 these terms connote greater or less specialization in organ for- 

 mation. Functionally, the same fundamental protoplasmic activi- 

 ties are present in all types, and the make-up of protoplasm, 

 whether in high or low types, is, so far as we can determine, 

 everywhere essentially the same. Chemically, protoplasm is a 

 mixture of proteins, carbohydrates, fats, salts of different kinds, 

 and water. The chemical and physiological activities of these sub- 

 stances between and among themselves and between them and the 

 environment constitute the dynamic manifestations of life, or 

 vitality. These are usually grouped into fundamental categories 

 of activity under the headings irritability, respiration, excretion, 



