MOLECULES AND STRUCTURE FORMATION 17 



DISCUSSION 

 A. G. Richards, D. F. Waugh, W. D. McElroy, W. J. Nickerson 



Dr. Richards (University of Minnesota): During development of an in- 

 sect's cuticle, there is a large dehydration of the chitin-protein matrix and a 

 simultaneous loss of almost all the salt, as shown by microincineration. Does 

 this imply that the salts, which are not homogeneously distributed in the cuticle 

 matrix, are nevertheless present effectively only in free solution in the water 

 phase? 



Dr. Waugh: The salts which are distributed heterogeneously are probably 

 not present effectively in free solution in the water phase. If we were sure 

 that there were no restrictions to diffusion and no active transport, the state- 

 ment could be made more positively. If this were so, it would appear that 

 during dehydration the binding sites responsible for heterogeneity effectively 

 disappear, leaving the ions to be swept out. 



Dr. McElroy (Johns Hopkins University): Is the water between fibrils 

 at such a low concentration that a limited chemical reaction could remove 

 essentially all of it? Are there good examples from biological structtires in 

 which the primary forces (van der Waals, H-bond, etc.) are only important 

 in bringing the molecules together? Do other chemical processes then occur, 

 which are important in giving the final property to the structure? 



Dr. Waugh: What kinds of fibrils? Usually there is too much water to be 

 removed by a limited chemical reaction. In this introduction, I have treated 

 the forces which are most likely to be operating in determining specificity of 

 interaction and structure formation. The final properties of the structure will 

 undoubtedly involve types of interactions and, particularly, chemical processes 

 not mentioned here; for example, the chemical processes involved in photo- 

 synthesis and bioluminescence. 



Dr. Nickerson (Rutgers University): Following up on the second of Dr. 

 McElroy's questions, do you have any information on the mechanism whereby 

 a trace of saturated fatty acid glyceride can induce almost instantaneous 

 crystalline order in a Hquid, unsaturated fatty acid glyceride? This reaction 

 appears, from some work in our laboratory on development of yeast cells, to 

 have a biological reality. 



Dr. Waugh: The fatty glvcerides undergo a series of phase changes with 

 temperature, and a sizable literature is available on this subject. It is possible 

 that a small amount of saturated fatty acid glyceride induces crystallization by 

 accelerating the formation of crystal nuclei. 



