4 STUDIES IN GELS 99 



mulae being very insensitive to changes in lengtii when this length is 

 large (Frey-Wyssling, 1937a). The experiments admit of no doubt, 

 however, that the length of the rodlets must be more - probably much 

 more - than 10 times as long as their thickness. 



4. From the arrangement of interferences can be derived the arrangement 

 of the rod-shaped lattice regions. In the diagram considered all rodlets 

 are parallel to the fibre axis {fibre diagram) ; but if they follow a screw 

 line within the wall, the interferences on the equator are drawn out 

 into sickles {.uckle diagram). Finally, if they lack all order, interference 

 rings instead of spots are obtained (Debye-Scherrer or ring diagram^ 

 see Fig. 69, p. 100). A comprehensive and simple treatment of the 

 relation between the arrangement of interferences and that of lattice 

 regions has been given elsewhere (Frey-Wyssling, 1935a, p. 11). 

 Ring, sickle and fibre diagrams are represented in Fig. 75, p. 106). 



Working out the fibre diagrams in full detail from the four points 

 of view mentioned, one arrives at the structural model of the fibre wall 

 shown in Fig, 59b (p. 77). This picture renders all the facts which can 

 be ascertained by means of X-rays, though the rodlets are in reality 

 much thinner. 



When drawing such a scheme it should always be borne in mind 

 that X-ray analysis only gives information about the regions of lattice 

 order; no information can be obtained in this way about the regions 

 without lattice structure. In particular, it cannot be decided by means of 

 X-rays whether the chain molecules in the crystal lattice are of exactly 

 the same length as the lattice regions or whether (as has already been 

 mentioned) they protrude from these regions without order and invade 

 several other lattice regions (Fig. 54, p. 70). X-ray analysis therefore 

 tells us nothing about the manner in which the crystalline regions are 

 interlinked or about the interstices between the regions of lattice order. 

 From a biological point of view, however, these intermicellar spaces 

 are of special importance. For, in most substances possessing a frame- 

 work, the micellar strands with their crystalline regions are to be con- 

 sidered as virtually lifeless, while all perceptible processes of life 

 presumably take place in the intermicellar system. Thus, the mechanical 

 properties of a gel are determined in the first place by the micellar 

 structure, whereas for all physiological questions (such as permeability, 

 metabolic processes, vital staining, etc.) one should study primarily 

 the intermicellar regions. 



