4 INTRODUCTION 



occur. The electron-optical images of biological objects should therefore 

 be considered critically. They must be compared with the results ob- 

 tained from the indirect methods and, in cases of contradiction, it must 

 be made clear on which side the error lies. In this way it has been 

 possible in some instances to show that the electron microscope had 

 produced spurious effects. Electron microscopy should not, therefore, 

 supersede the methods formerly appHed, such as polarization micro- 

 scopy or X-rays analysis, but the new direct method and the valuable 

 indirect methods must be used jointly, each acting as a check on the 

 other, in the exploration of the submicroscopic domain. 



The history of this science will soon be able to celebrate its first 

 centenary (Nageli, 1858). However, only in the last thirty years has 

 there been enough interest to produce a continuous development of 

 this field of research. For Ambronn, who devoted his whole life to 

 this branch of science and who published his fundamental researches 

 on the rod-Hke nature of the structural elements of gels in I9i6-'i7, 

 had to carry out his work, according to his own statement, "excluded 

 from publicity", and until his death in 1927 he considered that his 

 was the voice of a biologist crying in the wilderness. The general lack 

 of interest in submicroscopic problems was without doubt due to the 

 following. Colloid chemistry had developed into a general doctrine 

 of dispersoids. The discovery of the ultramicrbscope (Siedentopf 

 and ZsiGMONDY, 1903) had suddenly widened the range of the sub- 

 microscopic morphology of sols. With great enthusiasm biologists 

 mastered the new method, but discovered with disappointment that 

 nearly all important biological objects: cytoplasm, nuclei, plastids, 

 cell walls, etc. are "optically empty". We know now that this is due 

 not only to the close packing or the hydrophilic nature of the hypo- 

 thetical particles, but also, and mainly, to the fact that we have to deal 

 with anisodiametric structural elements, which are invisible in the 

 ultramicroscope if only one of their dimensions is amicroscopic, even 

 if such structural elements accumulate in loose meshworks of sub- 

 microscopic or even microscopic dimensions. This indicates that 

 biological gels do not at all represent disperse systems in the classical 

 sense of colloid chemistry (see Table II). The failure of the ultra- 

 microscope seemed to imply that these objects do not possess a sub- 

 microscopic structure. 



In the meantime, structural chemistry has developed amicroscopic 



