ITS CHEMICO-PHYSICAL AND MORPHOLOGICAL PROPERTIES 59 



in the water, its molecules separating from one another, and dis- 

 tributing themselves evenly throughout the water. 



Its power of swelling up and its non-solubility in water are 

 the most important properties of an organised body, without 

 which it is inconceivable that the vital processes could proceed. 



Many organised bodies may be dissolved if treated according 

 to special methods, as for example starch and gelatine-producing 

 substances, which become dissolved when they are boiled in 

 water. But even these starch and gelatine solutions differ very 

 much in their chemical properties from solutions of salt or sugar. 

 The latter diffuse easily through membranes, whilst the former 

 either do not do so at all, or only to a very small extent, whilst 

 their solutions are slimy or viscous. Graham distinguishes 

 between the two groups of substances, which exhibit such different 

 properties in solution, by calling them crystalloids and colloids. 



Now Nageli has attempted to explain all these phenomena as 

 being due to differences in the molecular structure of the various 

 bodies. As atoms combine together to form molecules, thus pro- 

 ducing so great a variety of chemical substances, so he considers 

 that the molecules unite together in groups to form still more 

 complex units, the micellrc, and that in this manner the complex 

 properties of organised bodies arise. In comparison with that of 

 the molecule, the size of the micella is considerable, although too small 

 to be seen icith the microscope ; it may be built up, not only of 

 hundreds, but even of many thousands of molecules. 



Nageli ascribes a crystalline structure to these micella?, in con- 

 sequence of their power of double refraction, which further is ex- 

 hibited by many organised bodies, such as cellulose, starch, mus- 

 cular substance, and even protoplasm itself in polarised light. In 

 addition, great differences may be present in their outward appear- 

 ance as well as in their size. 



The micellae have an affinity for water as well as for each 

 other; hence their power of swelling up. In a dry organised 

 body the micellae lie close together, being only separated by 

 delicate envelopes of water; as more water becomes absorbed, 

 these envelopes increase considerably in size, since at first the 

 micella^ have a stronger affinity for water than for each other. 

 Thus they become pushed apart from each other by the penetrating 

 water as with a wedge ; " however, organised bodies cannot become 

 really dissolved, for the molecular attraction of the micellae for 

 the water diminishes with distance at a projeortionally greater 



