Introduction 3 



Emulsion hypotheses of protoplasmic structure were favorably 

 entertained by biologists, but an emulsion satisfies very few of the 

 requirements of a living system, and fails utterly as a mechanical 

 basis of inost physical properties of protoplasm and elastic gels. 

 Emulsions do not take up water by imbibition, whereas protoplasm 

 does. Emulsions do not coagulate. Emulsions are not elastic as is 

 protoplasm. A mathematical analysis led Hatschek^ to the conclusion 

 that an emulsion structure of elastic gels is untenable. 



Biologists were misled by the presence in natural emulsions of a 

 stabilizer, a third substance, in addition to the water and oil of the 

 emulsion proper. It is this third substance, often a protein, which 

 exhibits the physical characteristics of protoplasm, and of jellies in 

 general, characteristics wrongly ascribed to a pure emulsion. Milk 

 illustrates the situation well. Superficially, milk is an emulsion of 

 butterfat dispersed in water, but when milk coagulates, the emulsion 

 plays no active part whatever. It is the stabilizing substance, a 

 protein, in milk which coagulates. And so it is with protoplasm. 



The introduction of the cytological technique of fixing and stain- 

 ing gave rise to numerous theories of protoplasmic structure based 

 on what was seen in prepared tissues. Much controversy developed 

 over the reality of these structures in living protoplasm, because 

 fixation produces artifacts. 



The fibrillar and reticular theories are the best known among 

 those based on classical cytological methods. Fibrillar and reticular! 

 structures in prepared sections of tissues may well be artifacts, but 

 an artifact is not without significance. The relatively coarse micro-l 

 scopic threads which form the visible fibrous entanglement or net, 

 may be artificially produced aggregates of threads of submicroscopic 

 dimensions. These latter are probably linear molecules. It seems 

 rather unlikely that a coarse fibrous coagulum should result from 

 the fixation of a fine granular suspension. Thus do the visible threads 

 of a reticulum in fixed dead material become evidence of submicro- 1 

 scopic threads in living protoplasm. 



The first hypothesis of protoplasmic and gel structure which held 

 the serious attention of chemists as well as biologists was the contri- 

 bution of the botanist Karl von Naegeli. He postulated molecular 

 aggregates of colloidal size. These aggregates Naegeli called micellae. 

 They might have a random distribution, or as later thought more 

 probable, a symmetrical arrangeinent, like bricks in a wall (Fig. 1) . 



'Trans. Faraday Soc. 12:17, 1917. 



