INTRODUCTORY 5 



divides, it produces other cells in all respects similar to the original 

 cell ; in the egg, however, repeated subdivision or segmentation 

 forms cells whereof some change into one kind of tissue and some 

 into another. The products of division of the amoeba therefore are 

 said to remain undifferentiated ; the products of segmentation of the 

 egg are said to differentiate, that is, to assume various forms and 

 functions. 



The functions apparently assumed by cells produced by segmen- 

 tation of the egg are not new developments, but are inherent in the 

 original egg as qualities of every living organ- 

 ized cell, serving to distinguish it from a par- 

 ticle of dead, unorganized matter. If we ex- 

 amine under the microscope an amoeba, we 

 observe (a) that it is a globular mass which 

 has the power of movement, and (b] that some 

 of the movements are the result of external 

 stimulation, and hence that it may possibly THE ORGANIC CELL> 



pOSSeSS Sensation aild Volition, Or will-pOWer. I, 2,. a parasitic amoeba- of the 



cockroach, magnified 1GO diame- 



Moreover, an amoeba will enclose within its ters - i,m the quiescent state: 2, 



in movement. 3, 4, a colorless 



own body adjacent particles of food, and, by wooa-corpuscie, soo diameters. 



3, quiescent: 4, in movement. 



changing them chemically, make them part 



of its own substance, and will reject whatsoever material it does 

 not need. Hence we conclude that an amoeba has the additional 

 functions of (?) absorption, (d) assimilation, and (e) excretion. We 

 are able to note further that to maintain life it needs a constant 

 supply of oxygen from the air ; hence we infer that it has the added 

 function of (/) breathing ; and, finally, we see it divide into two cells, 

 thus exhibiting the function of (g) reproduction. 



If we make a chemical analysis of the substance whereof the amoeba 

 is composed, we recognize it as protoplasm, the principal constituent 

 of every living cell, and a compound of carbon, oxygen, nitrogen, and 

 hydrogen. 



The round of life with an amoeba is, that under the influence of 

 oxygen its protoplasm is oxidized, or burned, with the consequent pro- 

 duction of heat and of energy of some kind (for example, movement), 

 and with the excretion of carbon dioxide and waste nitrogenous matter. 

 It repairs the loss of its protoplasm by taking to itself fresh carbon, 

 oxygen, nitrogen, and hydrogen from its food, casting out the resultant 



