PROTEIDS AND THEIR CLASSIFICATION. 879 



It is very desirable to select for them another name than nucleo-albumin, 

 since they contain no nuclein. Cohnheim suggests the name of phospho- 

 globulins or phosphoproteids. In addition to phosphorus these proteids. 

 usually contain some iron, but the amount is so small that it can scarcely 

 be present as a constituent part of the molecule. It seems more probable 

 that it is an impurity. Casein contains from 0.8 to 0.9 per cent, of phos- 

 phorus; vitellin, 1.31 per cent, of phosphorus and only 12 per cent, of nitro- 

 gen. These proteids have acid properties. They are not soluble in water, 

 but are very readily soluble in dilute alkalies. Their solutions are not coagu- 

 lated by heat. They show the usual proteid reactions and give the ordi- 

 nary end-products of hydrolytic cleavage upon digestion with proteolytic 

 enzymes or boiling with dilute acid. In the casein it has been shown 

 satisfactorily that no carbohydrate grouping is present in the molecule. 



Proteoses and Peptones. These names are given to the intermediate 

 proteids formed in the process of digestion by the proteolytic enzymes. They 

 may also be obtained by the hydrolytic action of acids or alkalies or by the 

 action of putrefactive organisms. If further hydrolyzed they split into some 

 of the amido-acids already referred to as constituting the end-products of 

 proteid hydrolysis. Since they are obtained most readily in peptic and 

 tryptic digestion, they have been supposed to be especially important in 

 the absorption of the proteid foods. They consist of smaller and more sol- 

 uble molecules than those of the proteids from which they are derived. 

 Many different kinds of proteoses have been described, but it is difficult to 

 assign absolutely distinctive characteristics to these compounds, since they 

 form a series of products intermediate between the original proteid and the 

 stage of peptones. The so-called peptones are characterized by their solu- 

 bility and the facts that they are not coagulated by heat and are not pre- 

 cipitated by complete saturation with ammonium sulphate. They give the 

 biuret (red) reaction as well as the xanthoproteic and Millon's reaction, but 

 are not precipitated by the mineral acids, trichloracetic acid, picric acid, 

 acetic acid and potassium ferrocyanid, etc. They are precipitated by phos- 

 photungstic or phosphomolybdic acid. The proteoses in general are dis- 

 tinguished by the following reactions: They are not coagulated by heat; 

 they are precipitated from their solutions by the addition of acetic acid and 

 potassium ferrocyanid ; they are precipitated by nitric acid and this precip- 

 itate dissolves on warming and reappears on cooling; they are precipitated 

 by saturation with ammonium sulphate and by all the so-called alkaloidal 

 reagents, namely, phosphotungstic acid, trichloracetic acid, picric acid, 

 tannic acid, etc. The proteoses form a group the members of which are 

 variously named. It is customary to speak of the primary proteoses (pro- 

 toproteose and heteroproteose) as distinguished from the secondary pro- 

 teoses (deuteroproteoses A, B, C). The former resemble more the native 

 proteids, while the latter approach the peptones. The distinction between 

 the primary and secondary proteoses is made chiefly upon the ease of pre- 

 cipitation. For example, the primary proteoses are precipitated by a lower 

 degree of saturation with ammonium sulphate and by nitric acid alone, 

 whereas the secondary proteoses require previous saturation with a salt 

 (sodium chlorid) before nitric acid will precipitate them, and they are precip- 

 itated by saturation with ammonium sulphate with much more difficulty, 

 some of them only after making the reaction acid. 



Protamins and Histons. The protamins have been obtained (Miescher- 

 Kossel) from the heads of the spermatozoa in fishes, in which they exist in 

 combination with nucleic acid. They differ considerably in the spermatozoa 

 of different animals, and are therefore designated according to the zoological 

 name of the fish from which they arise, as salmin, sturin, clupein, scom- 

 brin, etc. They show a biuret reaction, but in most cases fail to give Millon's 

 reaction. On hydrolysis they give some, but relatively few, of the usual 

 split products of proteids, and these largely the so-called diamido-bodies 

 (arginin, histidin, lysin) rather than the monamido-acids. Some of the latter 

 may occur, however, such as alanin, serin, amidovalerianic or a-pyrrollidin-car- 

 bonic acid. The protamins all give an alkaline reaction, form salts with acids, 

 and are precipitated easily. Their molecular structure is relatively simple. 



