The final product of food digestion as accomplished by pepsin with the hydrochloric acid of the gastric juice is peptone. Kuhne showed that peptone is seldom, if ever, pure in the stomach, but the substance produced is a mixture of true peptone with proteoses or albumoses, which have reactions that in many respects are similar. The albumoses are more highly diffusible than peptones. Undoubtedly both peptones and albumoses are formed during digestion, and both may be absorbed.

Albumoses, like peptone, give a violet colour when added to a dilute Fehling solution of copper sulphate, and on boiling with nitric acid they exhibit a yellow colour and a precipitate which alternately falls on cooling and disappears upon warming. The albumoses may be separated from peptones by complete precipitation by saturation in aqueous solution with sulphate of ammonium. Bauer states it as his belief (Dietary of the Sick) "that the peptones do fulfil in the organism all the functions of the albuminous bodies, since they are again turned into coagulable albumin"; but dissolved albuminates are not necessarily converted into peptones before they are capable of absorption (Voit and Bauer).

Politzer, Gerlach, and others have demonstrated experimentally that albumoses can support nutrition and even cause gain in weight when given alone and free from peptones, and Hildebrandt found that the nitrogen of albumoses artificially fed to animals was utilised in the nutrition of the body to an even greater degree than the peptones of meat.

An excess of proteids overworks the liver and produces, on reaching the general vascular system, various nervous disorders, and, it is believed by many, lithaemia and gout as well.