DETECTION OF PHOSPHORUS COMPOUNDS. 53 



molybdate reagent after having been kept several days, during 

 which it had deposited copious crusts of molybdic acid, gave, 

 when applied to sections from the same source, no such result, 

 the reaction proceeding in the slow progressive manner character- 

 istic of the phosphorus reaction as described by Macallum. 

 Again, in his investigation of the nature of the 'granule cells of 

 Paneth, Mr. Klein, working under my direction, found it neces- 

 sary to employ formalin in the fixation of the tissues in order to 

 preserve the granules. In preparations of this material treated 

 by Macallum's method, we were surprised to obtain a strong reac- 

 tion in the fibrils of the collagenic tissue of the tela submucosa. 



Clearly, the intense marginal reaction obtained in sections and 

 the early reaction obtained when freshly prepared solutions of 

 the nitric molybdic reagent were used could not be due to phos- 

 phorus. These anomalous characters of the reaction as applied 

 to sections could only be explained on the assumption that, 

 after the treatment with the nitric molybdic reagent, there existed 

 in the tissue compounds of molybdenum other than phospho- 

 molybdates, which gave the blue reaction with phenylhydrazin 

 hydrochloride. 



On account of the fact that the difference between freshly pre- 

 pared and older solutions of the nitric molybdic reagent is to be 

 found in the amount of molybdic acid contained, it seemed prob- 

 able that the extraordinary results of the reaction, as described 

 above, were due to the absorption of this substance by the tissue 

 elements. Accordingly, I undertook experiments to determine 

 the behavior of solutions of molybdic acid in reaction with 

 phenylhydrazin hydrochloride, as well as the capacity of the 

 tissue elements for absorbing it from its solutions. Later it was 

 found necessary to reinvestigate the reaction obtained by treating 

 ammonium molybdate in solution, and phosphomolybdate of 

 ammonium suspended in water, respectively with solutions of 

 phenylhydrazin hydrochloride. 



Although the experiments were started with the expectation 

 that a portion of the reaction would be found to be due to ab- 

 sorbed molybdic acid, I still thought at that time that the funda- 

 mental assumption was true, upon which the reaction was based, 

 namely, that the organic phosphorus was liberated from its com- 



