i-IJ.ci"o:i; 



dosa[4e and the organism, in any case, it will be irradiated. This, of 

 course, suggests the possibility of determining radiation effects on 

 localized areas of the nematodes and study of the resulting hereditary 

 results. 



Those of you interested in analytical work vull appreciate another advantage 

 of the X-ray microscopes of either the reflection or projection types. 

 X-ray diffraction patterns from selected areas of the specimens can be 

 obtained. Combined with X-ray photomicrographs, quantitative information 

 and specific element detection can be obtained about the composition of 

 small areas on the order of one square micron. 



}fy opinion is that the X-ray microscope probably would have more applica- 

 tions than the electron microscope in phytonematology for those situations 

 where magnifications and resolutions equal to those of the light micro- 

 scopes would suffice. At the present, we can only guess at the value to 

 microscopy of this new research tool. 



Visibility of Transparent Specimen Detail 



As previously mentioned, our problem in the microscopic study of nem.;-^todes 

 is not one of magnification alone. The study of the nematode is essen- 

 tially examination for fine details in a transparent material. The well- 

 known solutions to this problem ordinarily involve one or more of the 

 following: Staining of the specimen. This is done only with difficulty 

 with fixed nematode specimens and is rarely satisfactory with intra vitam 

 stains. Staining of fixed specimens presents additional problems of 

 distortion, artifacts, and considerable consumption of time. Substage 

 diaphragm adjustments are very helpful in improving the visibility of 

 otherwise nearly transparent specimens. Despite the theoretical disadvan- 

 tages through reduction of resolution, marked injjrovement in many struc- 

 tural details of the nematodes result, but there is no denying the loss 

 of definition of very fine structures. Incidently, stopping down the 

 substage iris results in a sort of phase or interference type of illumi- 

 nation. Darkfield illumination and polarized light have, of course, been 

 tried, but for certain special applications they have not been found of 

 value in improving what one can see of nematode structure. 



Before going into some of the newer ways of making the invisible visible, 

 a few words of explanation regarding visibility may prove helpful. The 

 normal colorless or monochromatic microscopic object is seen because it 

 has regions of varying optical density which the eye detects as differ- 

 ences in light intensity. In normal brightfield illumination a completely 

 transparent specimen is very difficult to see in any detail, as all of its 

 parts are equally dense. In darkfield illumination the light illaminates 

 the object from an oblique angle and the completely transparent specimens 

 show up due to their scattering and diffraction of the light. Generally, 

 the surface layers, rather than the internal details, are revealed, and 

 there is an exaggeration of the contrast. In polarized light the com- 

 pletely transparent structure becomes visible if it has light directionol 



