324 NITROGENOUS HI.STOGENETIC SUBSTANCES. 



been sufficiently investigated; but among them are always to be 

 found carbonate, butyrate, and valerianate of ammonia, sulphide of 

 ammonium, leucine, and tyrosine. 



It is further worthy of observation that all histogenetic sub- 

 stances are invariably accompanied with fats., alkalies, and salts of 

 lime, from which it is impossible or very difficult to separate them 

 without decomposition. It is not improbable that in the majority 

 a portion of these admixtures is chemically combined with them ; 

 and although but few of these chemical combinations, as that of 

 casein and phosphate of lime, admit of actual demonstration, many 

 chemists are disposed to regard a part of these adhering matters 

 as chemically combined, since the most ordinary indifferent 

 solvents are unable to separate them, while the more powerful 

 agents exert a decomposing or at least a metamorphic action on the 

 main substance ; and this applies more especially to the mineral sub- 

 stances accompanying these matters. Rose's investigations* re- 

 garding the mineral substances, have recently given greater weight 

 to the idea that they may in part at least be combined in a non- 

 oxidised condition with nitrogenous bodies, as has long been 

 conjectured, in accordance with Mulder's views, to be the case with 

 the sulphur, and in part also with the phosphorus of these substances. 

 Rose has advanced very satisfactory grounds for believing that a 

 portion of the alkalies and alkaline earths is contained in these 

 matters in a metallic condition, and combined with radicals con- 

 taining phosphorus and sulphur. We purpose, however, reverting 

 to this subject under the head of " the mineral substances of the 

 animal body." 



It may easily be inferred from the abovenamed properties, that 

 it is extremely difficult or perhaps quite impossible to exhibit these 

 bodies in a chemically pure condition. 



By their not crystallising, and by their not volatilising without 

 decomposition, we are deprived of two most important means of 

 readily isolating them from other substances ; while the readiness 

 with which they are decomposed, has hitherto prevented us from 

 ascertaining which of the above mineral substances are chemically 

 combined, and which are simply mixed with them. This refers spe- 

 cially to the soluble bodies of this class, as albumen, casein, &c., none 

 of which have as yet been exhibited in a chemically pure soluble 

 form. We are still more in doubt in reference to the insoluble 

 substances deposited in the tissues ; for even if we succeed (which 

 we rarely can) in extracting from them all mineral substances, we 

 * Ber. d. Akad. d. Wiss. zu Berlin. Decbr. 1848, S. 455-462. 



