40 FUNDAMENTALS OF SUBMICROSCOPIC MORPHOLOGY I 



kinds of different molecules containing hydroxyl groups can combine 

 with glucose according to both these schemes, which are then dis- 

 tinguished as a- and /?-glucosides respectively. This distinction is 

 not only interesting and important from the point of view of molecular 

 morphology (structural chemistry), but is also of great importance in 

 physiology. In fact, the a- and /3-bridges are broken down by quite 

 different enzymes. For the hydrolysis of maltose we need an a- 

 glucosidase, which is not capable of splitting cellobiose, while, con- 

 versely, ^-glucosidases can attack cellobiose but are inactive with 

 respect to maltose. It seems that in plants the reserve substances, 

 which mus" be quickly mobilized when required, are more often built 

 according to the a-type (saccharose, starch), while glucosides, which 

 cannot be used directly as reserves (e.g., amygdalin), and cellulose 

 are /5-glucosides. This example shows that ultimately the problem 

 of enzymes is also of a morphological nature. To be able to distinguish 

 between an a- and a /5-bond, they must possess a quite specific struc- 

 ture. Without a knowledge of this structure, it is unlikely that the 

 riddle of organic catalysis will be solved (Mittasch, 1936). The well- 

 known comparison of the lock and the key is not merely a symbol, but 

 substrate and enzyme must fit together in the strict sense of the word 

 as two parts which are adjusted morphologically to each other. 



c. Structure of Phase Boundaries 



Surface tension. The regions containing phase boundaries are always 

 inhomogeneous. One can only speak of homogeneous phases if in 

 comparison with their surface they are so extended that all surface 

 effects can be neglected. 



These inhomogeneities are best known in liquids, where they 

 manifest themselves as surface tension; but they also occur, although 

 less markedly, at the surface of crystal lattices or at the boundary of 

 gaseous phases. The surface tension of a liquid is caused by the fact 

 that the molecules in the bulk of the phase are surrounded on all sides 

 by similar molecules, whereas in the phase boundary this only occurs 

 on one side. If, by way of example, we consider a liquid-gas boundary 

 layer, the attractive forces of the small number of gas molecules avail- 

 able can at a first approximation be neglected; therefore, at the surface 

 the molecules are subject to a quite different field of cohesive forces 

 from that to which those inside the liquid are exposed. 



