The red corpuscles of the blood have a very large content of hemoglobin. When human blood is dried, the proper pro portion of hemoglobin in the red corpuscles is found to be about 94 per cent. Either acids or alkalis reduce hemoglobin to the histone globin and the iron compound hematin, which is not a protein, but a derivative of pyrrole, one of the decomposition products of the proteins.
Albuminates belong to the group Metapro teins. They result from the so-called ((acid albumin,)) obtained by treating an albumin or a globulin with dilute acetic or hydrochloric add. Acid albumin is soluble in dilute acids or alkalis, but insoluble in a neutral mentsruum. When the original protein is treated with a small quantity of dilute alkali, it combines with the alkali to form ((alkali and this, like acid albumin, is soluble in weakly acid or alkaline media, but insoluble in a neutral one. Alkali albumin is likewise not coagulable by heat. The combinations here described may be taken as typical of the albuminates in a general way; but as the albuminates are doubtless very numerous and as they have not yet been fully investigated, it must not be inferred that they will all possess the characteristics of ordinary acid and alkali albuminates.
Proteoses and Proteins de rived from the albumins or globulins or al buminates by the action of digestive ferments, such as pepsin and trypsin. They are interme diate between the original proteins and the pep tones into which these original proteins are ultimately transformed by the digestive fer ments. They are precipitated from solution by nitric acid, the precipitate dissolving upon ap plication of heat. They are also somewhat
diffusible, but not to the same extent as the peptones.
Proteins which are formed by the prolonged action of digestive ferments upon other proteins. (Compare the proteoses in the preceding paragraph). While they are not precipitated by heat, nor by nitric acid, they are precipitated by tannin and by certain other reagents. It seems quite clear that peptones are polypeptids. The peptones are diffusible and they play an exceedingly important part in digestion and assimilation. Peptones that are artifically prepared are commonly hitter, perhaps from the development of alkaloids or glucosides. Pure peptone has a meaty flavor.
The majority of peptids dissolve readily in water but not in alcohol. A few which are almost insoluble in water dissolve in acids or in alkalis. Most of them have a bit ter taste. When heated with concentrated hy drochloric acid for several hours they are com pletely resolved into amino-acids.
Through this system of investigation it is hoped ultimately to discover the process of the upbuilding of the whole class of proteins from their primal elements.
Cathcart, E. P., 'The Physi ology of Protein Metabolism) (London 1912); Mathews, A. P., 'Physiological (New York 1915) ; Osborne, T. B., 'The Vege table Proteins) (London 1909) ; Plimmer, R. H. A., 'Chemical Constitution of the (2 vols., London 1912-13), and 'Practical Or ganic and Bio-Chemistry> (London 1915); Robertson, T. B., (The Physical Chemistry of the Proteins) (London 1918) ; Schryver, S. B., 'The General Character of the Proteins) (Lon don 1909).