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THE AMERICAN NATURALIST [Vol. LIII 



under the existing pressure and temperature, this transformation will be 

 "suspended" or delayed, and the system will become metastable (that is 

 temporarily stable as long as it is not brought in contact with the new 

 phase). Only in the case of the formation of the liquid from the solid 

 phase, in a one-component system, has this reluctance to form a new 



To ensure the formation of the new phase, it is necessary to have that 

 phase present. The presence of the solid phase will prevent the super- 

 formation of the metastable phase, quantitative measurements have been 

 carried out only in the ease of the initiation of crystallization in a super- 

 cooled liquid. As the result of these investigations, it was found that, in 

 the ease of superfused salol, the very small amount of 1 X IQ-i gm. of 

 the solid phase was suflTieient to induce crystallization. Crystallization 

 of the supercooled liquid, however, can be initiated only by a " nucleus " 

 of the same substance in the solid state; ... it is not brought about by 



The following illustration is of interest in this connec- 

 tion. From a saturated solution of anhydrous sodium 

 sulphate, Na2S04, at 24° C. different compounds may be 

 obtained by seeding with different crystals. If a crystal 

 of the heptahydrate, NaoSOj-THoO, is added, this salt 

 crystallizes out ; if a crystal of the decahydrate kno-svn as 

 Glauber's salt, NasSO. lOHsO, is added, Glauber's salt 

 crystallizes out. In this case both the solution and the 

 heptahydrate are metastable. It should be noted that the 

 seeding accomplishes two things: (a) it induces crystal- 

 lization and (b) determines the nature of the crystals. 

 Moreover since the crystals produced are hydrates, they 

 represent products of synthesis. 



Ill 



Living organisms accordingly perform two processes, 

 behavior and assimilation, and depending on whether the 

 one or the other process is considered, they present fun- 

 damentally different aspects. If we make a cross-section 

 (to borrow an expression of E. B. Holt) through the or- 

 ganism in one direction, it appears as a system in equi- 

 librium obeying the theorem of Le Chatelier. If we make 



