ON THE MICRO-CHEMISTRY OF CELLS. 311 



acetic acid it gives an instantaneous precipitate of tlie iiexanitrite of cobalt 

 and potassium, K3CO(N02)6, carrying down with it a certain quantity of 

 the precipitant, ]Sra3C0(N0,)c. So completely is the potassium removed 

 from solution that the reagent is found to be of service ^ as a means of 

 separating the element from the other alkalies and the alkaline earths in 

 the quantitative estimation of potassium. The precipitate hi but very 

 slightly soluble in water, which may therefore be used to remove the 

 excess of the precipitant, after which the precipitate may be washed with 

 a solution of sodium nitrite to which acetic acid has been added, or with 

 a solution of sodium acetate. In either of these solutions the precipitate 

 is practically insoluble, and is thereby freed from traces of the corre- 

 sponding ammonium compound, CO(NH3)3(N02)6, which is much more 

 soluble than the potassium compound. 



This reaction does not precipitate the amido acids, glycin, leucin, taurin 

 tyrosin, sarcosin, aspartic acid, or glutamic acid, nor does it precipitate urea,, 

 carbamic acid, asparagin. These therefore do not complicate the reaction, 

 and the only compounds in living protoplasm which, in addition to those 

 of potassium and ammonia, precipitate with the reagent are creatin and 

 oxalic acid. The former separates out from solution only slowly, and not 

 at all if solution is very dilute. As it does not occur in the vegetable 

 cell, and is unknown in the tissues of invertebrates, it cannot confuse the 

 determination of the presence of potassium. The distribution of oxalic 

 acid and its sales is so limited that they cannot interfere with the success 

 of the reagent in localising potassium in the cell. 



The hexanitrite of cobalt and potassium is brownish yellow, and, 

 therefore, except when it is abundant, not readily recognisable directly. 

 It is brought into view by treating the preparation with ammonium 

 sulphide, which reveals the presence of the potassium through the black 

 sulphide of cobalt, CoS. If at the same time it is mounted on the slide- 

 in dilute glycerine, to which a trace of ammonium sulphide is added, it 

 will keep unimpaired for a few weeks. 



Some of the results of the investigation with this reagent are espe- 

 cially interesting in that they directly negative the generally accepted views- 

 as to the distribution of the salts of the alkalies in the cell. 



1. As a rule the nucleus is free from potassium, even when the cyto- 

 plasm contains it in abundance (the intestinal epithelium of insecta and 

 Crustacea, the erythrocytes of amphibia). In algaj the nucleus of the 

 healthy cell never contains potassium, and even in karyokinesis the chro- 

 matic filaments are free from it, however abundant it may be in the 

 cytoplasm. In such non-nucleated forms as the cyanophycefe the ' central 

 body,' which is regarded by cytologists generally as the homologue of the 

 nucleus of higher forms, is also absolutely free from potassium, although it 

 may occur in abundance in the peripheral zone, and particularly in the 

 so-called ' red granules ' of Biitschli. 



2. The salts of potassium when abundant in the cytoplasm are not 

 uniformly diffused through the latter. In the vegetable cell as a rule 

 only a minute quantity is so diffused, while the I'est is localised apparently 

 as precipitates in portions of the protoplasm w-hich serve as inert structures, 

 and these ai-e situated adjacent to the cell membrane (algsc). In this 

 respect the salts of potassium are disposed of like those of iron when the 



' Van Leent, /r^eit. fiir anal. Ckemie, voL x\. 1901, p. 567; also Antenrieth and 

 Bernheim, Zcit. fiir jjhysiol. Cheniie, vol. xxxvii. 1902, p. 29. 



