266 C. NEUBERG, A. GRAUER VOL. 12 1I953) 



An ideal method would be the histochemical characterization of specific cell ingredients 

 by local fixation through specific precipitation reactions. Nucleic acids may thus be 

 characterized according to Opie and Lavin* by suitable application of La-acetate. The 

 latter will form a compound with ribonucleic acid which will withstand the action of 

 ribonuclease whereas basophilia of the original substance will be retained. 



The reactions of nucleic acids with the salts of various rare earths have long been 

 known and recommended for characterization of nucleic acids^ The fate of radioactive 

 lanthanum has been studied by Ekstein and Lewin^, Wurm^ and Stern et al.^ in normal 

 as well as pathological tissue. 



We have investigated the specificity of suitable precipitation reactions. In consider- 

 ation of the problems of radioautography, we studied the precipitability of natural 

 substances mainly by salts of the elements thorium, lanthanum and uranium. The 

 initial data could be obtained by means of the natural, only slightly radioactive metal 

 compounds. Salts of the rare earths as well as of thorium and uranium with various or- 

 ganic substances have been prepared years ago mainly because they represented a cer- 

 tain analytical and preparative interest. (For details see the manuals.) The large number 

 of important cell constituents, ingredients of tissue liquids and metabolites which are 

 precipitated by the above metal salts over a wide range of pH constituted somewhat of 

 a surprise. 



These salts will precipitate aliphatic, hydroaromatic and aromatic acids as well as 

 certain amino acids, peptides and peptone-like substances in addition to special plant 

 constituents such as aliphatic and cyclic polyhydroxy-acids. 



It seems remarkable that some of the most significant phosphorylated intermediates 

 of carbohydrate metabolism are precipitated rather completely. Phytates and the nucleo- 

 tides are precipitated as well as the nucleic acids. It also seems noteworthy that all 

 products of the di- and tri-carboxylic acid cycles are precipitated. Details are shown 

 in the following tables. 



This precipitability of numerous naturally occurring substances by the above- 

 mentioned metal salts— and that number may be further considerably increased — -might 

 be used in micro-chemical methods of determination. Results obtained by this method, 

 however, should be carefully interpreted since there is no specificity as such. Specificity, 

 on the other hand, may be frequently obtained by combining the radioactive forms of 

 the above metals with the substances to be precipitated labelled with regard to various 

 elements. Thus a number of possibilities might be developed for purposes of radioauto- 

 graphy^. With different types and intensities of radiation even the more simple criteria 

 such as provided by the Geiger counter might prove adequate. 



The precipitation reaction is highly sensitive (for limits see later). If there is no 

 direct flaking of distinct particles, adsorption will jirovc successful. Suitable adsorbents 

 for analogous purposes have previously been recommended^''. Obviously these materials 

 must be free of radiating isotopes. The chromatographic separation of substances of 

 similar precipital^ility has of course been successfully carried out and described j)ri'- 

 viously. 



The principle of double and multiple hibelling is applicable also in tlie precipitation 

 of inorganic salts (see later). 



References p. 2y2. 



