332 



THE AMERICAN NATURALIST [Vol. LI 



The essential feature of the above described mechanism 

 for the antocatalji;ic production of polymeric molecules 

 may be illustrated to the eye by means of a model con- 

 sisting of a board with a large number of small compass 

 needles mounted upon it. If these needles are freed from 

 the action of the terrestrial magnetic field and are then 

 shaken into a random orientation, they may remain in this 

 condition indefinitely. However, if a small number of 

 adjacent needles be turned by some outside force so as to 

 acquire a common direction, their combined magnetic 

 fields will cause other neighboring needles to swing into 

 line, so that the action must spread to all of the needles 

 on the board. The field of an ideal compass needle has a 

 simple bipolar pattern, and a symmetrical distribution of 

 forces. In the cases of specific atoms and molecules, how- 

 ever, this is probably seldom true. Nevertheless, the 

 general principles involved in their dynamic interaction 

 would remain the same as those for the case of the com- 

 pass needles. 



It is clear that the explanation of autocatalysis above 

 given accoimts immediately only for the synthesis of poly- 

 iiu'i-ic nu)l( ciilc- from individual units which are all alike. 

 A> a nilc, clioiiiical changes involve the interaction of dif- 

 ferent units, and it can easily be seen that the same gen- 

 eral mechanism will apply to the catalysis of reactions of 

 this sort as to that of simple crytallization. The prin- 

 ciples involved in the process have been made especially 

 clear in the recent articles of Langmuir.^'' Consider first 

 a solution containing two kinds of molecules which can be 

 deposited upon a crystal surface consisting of an orderly 

 arrangement of these two molecular groupings in mosaic 

 or lattice form. The second species of molecules may be 

 considered, for example, to be those of the solvent, as in 

 the case of "water of crystallization." There will be cer- 

 tain '^elementary spaces"— as Langnuiir calls them — 

 upon the surface of the cry.tnl. whirli will I'^iKM-ially at- 

 tract and orient the water iiiolfciih's. and adjacent ele- 

 mentary spaces which will act in the >anu^ way upon the 



