Differentiation. 275 



of the plant thus set free to become an animal has this chance only for 

 a livelihood ; viz., since it has cut loose from the plant where it was as- 

 sociated with Chlorophyl cells which had the power to gather all the 

 starch required for the protoplasm of the plant, it must now meet with 

 starch which has accidentally become separated from the leaves of plants, 

 or with juices or particles more or less digested and now lying around 

 ' loose. If it fail to find this food ready made it must starve to death, 

 for it is nothing but an adventurer, a tramp. If it meet with such food 

 it crawls over it, and while thus in contact with it, the diastase separates 

 it into the glucoses which are then taken up by the hungry and ex- 

 hausted molecules composing the animal. The case would be some- 

 what different if the escaped protoplasm should have some cells of 

 chlorophyl in partnership with it, for then it would have the same re- 

 source as the stationary plant has of getting its starch from the carbonic 

 dioxide of the air. It would have two resources, that of the chloro- 

 phyl, and also the chance of meeting ready made food. As stated at 

 the end of Chapter 24, there are a number of animals thus equipped 

 with the Chlorophyl cells and so having the double resource. The de- 

 pendence upon ready made food involves one of two contingencies ; the 

 food must either be brought to the animal or he must go to it. If he 

 gets enough food by either means, or both, the necessity to use the 

 chlorophyl function will be obviated, and falling into disuse will after 

 a time become aborted and the cells will disappear. If the condition of 

 the food supply requires the animal to habitually move to it, his locomo- 

 tive powers will be improved and locomotive organs finally differentiated. 

 We are not to suppose that there is any preconceived purpose in the 

 locomotion of a protozoan any more than in the movement of sap in the 

 stem of a weed. Heat and light constitute the motive force in the 

 movement of the protoplasm of the plant, and so they continue to do 

 after the protoplasm is liberated from the plant. The matter of meet- 

 ing with food in its perambulations, however important to the Amoeba, 

 is purely incidental. But having met with it, if there be unsatisfied 

 chemical affinities in any of its molecules, the food will be absorbed. 

 As soon as the chemical affinity is satisfied by the introduction of the 

 food, the oxygen of the air proceeds to disturb it again by seducing 

 atoms of carbon from the molecules of the organism, burning them up 

 and forming carbonic dioxide as an excretion. The heat thus developed 

 in the organism becomes the electrical energy which contracts the pro- 

 toplasm and causes it again to move. No doubt both the light and heat 

 of the sun also contribute directly to this end as well as indirectly. 

 Thus the protoplasm of the amoeba constitutes a machine capable of be- 

 ing moved by forces outside of itself. If it be not in contact with nu- 

 tritive substances, or if it lose the association of chlorophyl, this quality 



