502 Annals New York Academy of Sciences 



with the Schiff's reagent. Therefore, the development of a magenta color 

 with the Feulgen reaction is, in this instance, not specific for DNA. 



Similar results were obtained with the PAS reaction. There seemed to be 

 no additional staining produced when samples were treated with periodic acid 

 before reaction with Schiff's reagent, as compared with reaction with Schiff's 

 reagent alone. Attempts to inhibit the staining produced by Schiff's reagent 

 by previous treatment of samples with aniline chloride and hydroxylamine, to 

 block the aldehyde groups,'^ were only partly successful in the samples and in 

 periodic acid treated starch controls. Hence, the nature of the reactive groups 

 is not known at present. 



The presence of DNA in the organized elements would be powerful evidence 

 of their biologic origin. Because the results of the Feulgen reaction had been 

 interpreted in published reports as indicating the presence of nucleic acid in 

 the meteorite,^-* it was desirable to confirm this interpretation with another 

 histochemical test for DNA. Methyl green is freciuently used for this purpose.^' 

 The characteristic reaction of DNA with this stain is thought to be the result 

 of binding of the dye by phosphoric acid radicals in the intact, polymerized 

 DNA.* Thus, the mechanism of this reaction is altogether different from that 

 of the Feulgen reaction. 



Samples of rat spleen, Orgueil and kimberlite were stained with methyl 

 green.* As a control procedure, samples were treated with 10 per cent per- 

 chloric acid for 4 hours and 30 minutes, a procedure which depolymerizes and 

 extracts DNA from biological samples.'-' In rat spleen sections stained directly 

 with methyl green, there was brilliant green staining of the nuclei (figure 4, B). 

 In spleen sections treated with perchloric acid to remove DNA before reaction 

 with methyl green, there was no nuclear staining (figure 4, E). However, 

 the samples of Orgueil and kimberlite stained brilliantly with methyl green 

 whether treated previously with perchloric acid or not (figure 4; A, D, C, F). 



It is evident that when biological staining reactions are applied to nonbiolog- 

 ical materials, great care is necessary in the interpretation of results. Because 

 of the presence of other reactive groups the usual tests for DNA are no longer 

 specific. Positive or negative reactions of any DNA present would be masked 

 by the intense, nonspecific staining due to other groups. Under these condi- 

 tions, the staining tests cannot be regarded as evidence for the presence of 

 DNA in the meteorite. 



Treatment with Hydrofluoric Acid 



The "organized elements" were reported by Nagy el at., not to be seriously 

 affected morphologically by treatment with boiling hydrofluoric acid (HF) for 

 15 minutes, whereas silicate minerals should be dissolved.- We treated a 

 sample of Orgueil with boiling HF for 15 minutes; 49 per cent of the sample 

 remained (tabi.e 3). Because the carbon content of the meteorite is only 3.1 

 per cent, the bulk of this residue must have been inorganic. Consideration of 

 the pertinent solubility products indicates that calcium, magnesium, and 

 possibly other major constituents of the meteorite should remain as insoluble 

 fluorides or fluosilicates. Thus, persistence after HF treatment is not a suffi- 

 cient criterion for the organic nature of a particle. 



To dissolve the mineral residue, the sample was first treated with HF for 17 



