68 RALPH S. LILLIE. 



through similar transformations; eventually in place of the orig- 

 inal cell there are thousands. The non-living material of the 

 culture medium consisting of water, sugar, ammonium tar- 

 trate, and inorganic salts of potassium, calcium, iron, and mag- 

 nesium has been transformed into complex and active living 

 protoplasm of a specific chemical and structural organization. 

 Each living cell exhibits the "germ-action" so characteristic of 

 life- i. e., acts as a center of chemical and physical transforma- 

 tion of a definite kind by which more and more yeast protoplasm 

 is formed. We may note here the analogy- to which we shall 

 return with the process of specific accretion by which a crystal 

 introduced into a super-saturated solution increases its size and 

 becomes a center of deposition of more crystals of the same kind. 

 But the analogy is incomplete; the living organism does not 

 merely change the physical state of the substances which it 

 takes in from the surrounding solution; it also modifies them 

 chemically in the most profound manner, and from the above 

 simple materials it builds up proteins, lipoids, fats, glycogen, 

 and a multiplicity of other substances not present in the culture 

 medium. Further, not only are these substances synthesized, 

 but they are distributed throughout the growing mass of proto- 

 plasm in a perfectly definite manner, partly as solid structural 

 material, partly as dissolved or other material serving for energy- 

 production or some form of metabolism. 1 Each one of the specific 

 organized structures thus produced, the yeast cells, reduplicates 

 the physiological activities as well as the structural characters of 

 the parent cell. The result is that the non-living material of 

 the surroundings is transformed or worked over into organized 

 living material of a predetermined type, i. e., the transformation 

 is specific and depends upon the nature of the germ originally 

 introduced into the medium. Both growth and heredity are 

 exemplified in their simplest manifestations; and we see again 

 that these terms do not signify two objectively different pro- 

 cesses, but merely two aspects of the same process "growth," 

 the quantitative term, denoting the increase in the total mass of 

 living substance, while "heredity" emphasizes the specificity 

 of the process and its dependence upon the parental character. 



1 7. e., the problem of differentiation is inseparable from the problem of growth. 



