Fitch & Anders: "Organized Elements" in Chondrites 509 



under ideal conditions is only 0.2 to about 0.3 fx for the objectives that must be 

 used with this sort of preparation. Akhough the organized element illustrated 

 by Nagy et al.~ had to be viewed through a layer of optically imperfect mag- 

 nesium sulfate, the presumed spines illustrated in the drawing were spaced 

 only 0.3 yu apart. 



Judging from both visual inspection and the published illustration [tigure 4d 

 in reference 2] this organized element appears to be opaque. Previously, it 

 was emphasized that all organized elements in crushed preparations were 

 transparent.^ - Also, none of the particles in the thin sections seems to have 

 the highly structured morphology, although about 8000 organized elements 

 should have been present in a thin section I4 inch in diameter and 20 yu in 

 thickness. 



Some organized elements in the thin sections were described as having pink 

 fluorescence [tigure 5 in reference 2]. We encountered occasional particles in 

 crushed preparations which appeared red against the dark background when 

 illuminated with ultraviolet light. However, this did not prove to be true 

 fluorescence. These particles when viewed with polarized visible light were 

 doubly refractile. The fluorescence microscopes commonly used in biological 

 investigations use darkfield illumination. The usual light source is a high 

 pressure mercury arc with various filters placed in the light path to absorb the 

 visible light. All of the 5 filters commonly used transmit ultraviolet and some 

 blue light but they have an appreciable transmittance in the red portion of the 

 spectrum as well.'^ Hence, doubly refractile particles should be expected to 

 appear red when viewed with ultraviolet light in the fluorescence microscope. 



Perhaps additional study of thin sections will reveal particles with a more 

 conclusive combination of properties.* In our opinion the present evidence is 

 inadequate to suggest a biological origin for the indigenous particles. 



Discussion 



Several features make it difficult to accept the highly structured particles as 

 extraterrestrial in origin. They are absent from our preparations of Orgueil, 

 although material from the same stone was used. They have not been ob- 

 served in thin sections, and they often show a morphological resemblance to 

 common airborne contaminants. Although a strong case can be made for the 

 biological origin of some of these structures, the probability of a terrestrial 

 contamination has not been ruled out in their case. 



The situation is altogether different in the case of the small, brownish-yellow, 

 somewhat irregular, roughly spherical grains which apparently make up most 

 of the 1700 particles per milligram reported previously by Claus and Nagy^ 

 and Nagy ei air Although our own experience suggests that this number 

 represents an appreciable overestimation, there is no doubt that such particles 

 do exist. 



They are undoubtedly indigenous to the meteorite, but their morphology is 

 so featureless that an inorganic origin cannot be ruled out. None of the other 



* Additional observations on thin sections are reported in another paper (Anders and 

 Fitch, Science, in press). 



