THE DOMAINS OF MORPHOLOGY 3 



look at the bottom through the water above it. He must not cUng 

 stubbornly to the rocks on the shore but must free himself from the 

 land. He must "swim", and from the surface of the water must find 

 out indirectly with a plummet how the bed is shaped. Each fathoming 

 provides him with a point, and the profile of the bed can then be 

 constructed by interpolation. 



Until recent times, in the submicroscopic domain which lies beyond 

 the microscopic limit, the situation was completely analogous. Views 

 on submicroscopic morphology could be obtained only by sounding, 

 i.e., by indirect means, and the invisible shapes and sizes could be 

 deduced only from a combination of the various methods of research. 



The discovery of the electron microscope after 1938 suddenly 

 brought the submicroscopic regions within reach. By means of electron 

 rays the resolving power has been increased a hundredfold in one 

 sudden leap. The surface of the water in the lake to be studied has, so 

 to speak, been reduced to a much lower level. The precipices and gullies 

 which had hitherto been hidden have become accessible to the in- 

 vestigator, who is now equipped with the means whereby he can move 

 about in this difficult province. Submicroscopic morphology has 

 accordingly lost something of its mysterious charm. The unravelling 

 of its secrets no longer wholly depends upon an ingenious com- 

 bination of partial evidence obtained indirectly, as it still does in the 

 study of the constitution of organic molecules in structural chemistry. 

 There is now a direct means of checking the conceptions developed 

 so far. The objective micrographs given by the electron microscope 

 have made submicroscopic morphology very popular in biology, 

 whereas formerly it had been left to those few biologists with a working 

 knowledge of physics. 



However, the electron microscope cannot completely replace the 

 indirect methods which have been so successful up to now. All 

 specimens have to be dried and this may cause serious artefacts in 

 structures like protoplasm containing 80 to 90 % water, and there 

 exist many objects which, for technical reasons, cannot yet be imaged 

 in the electron microscope; furthermore, irradiation by electrons 

 represents a bombardment which, compared with irradiation by light, 

 involves incomparably greater energies. These are apt to destroy the 

 structures of specimens cut into insufficiently thin sections. Amicro- 

 scopic structures, invisible in the electron microscope, may, moreover. 



