124 PHYSIOLOGY 



The infinite variety that exists in nature is mar- 

 velous, but the infinite unity is much more marvelous. 

 A multitude of animals and plants, each with its own 

 peculiarities, exists, but the same life processes depend- 

 ent upon the same simple principles, are found in them 

 all. And the manner in which these are manifested is 

 the whole of physiology. It has been customary to 

 emphasize the differences that exist between organisms, 

 but emphasis should rather be laid upon their similarity. 



All organisms are composed of protoplasm, or living 

 matter. What this protoplasm is we know only in part. 

 We can analyze it chemically after killing it and thus 

 find what elements are present in dead protoplasm. 

 But what the subtle thing is which distinguishes this 

 dead protoplasm from living protoplasm we do not 

 know. Living protoplasm has the power to move, to 

 grow, and to reproduce ; and in this respect the pro- 

 toplasm of the simplest animals and plants in no wise 

 differs from the protoplasm of the highest animals and 

 plants. The essential processes of physiology go on 

 in the ameba as perfectly as in human beings, although 

 the ameba is but a single cell not even possessing a 

 definite cell wall. It can move from place to place; 

 it can take in food and oxygen, carry these to any and 

 all parts of its body and out of them make new 

 protoplasm ; it can give off waste materials, and it can 

 produce its own kind. Physiologically human beings 

 can do no more. 



All living things may be divided into two classes, 

 animals and plants. It seems easy to distinguish these 

 from each other, for the higher forms that we meet 



