ABSTRACT
Chemists and physiologists between them have been so busy that they are able to distinguish and characterise some fifty substances which are gathered under this name. Some of these are familiar enough in white of egg, in the serum of blood, in milk, in animal cartilage, bone, and horn, in the gluten of wheat flour, and in many seeds such as peas, beans, and almonds. The large number of apparently distinct compounds which, presenting as they do few of the characters by which pure chemical individuals are usually recognised, renders the investigation of the proteins one of the most difficult tasks undertaken by the chemist. The simple proteins and the conjugated proteins are all substances which are supposed to exist in the tissues and juices of animals and vegetables. They are separated by taking advantage of their solubility or insolubility in saline solutions, such as aqueous ammonium sulphate or sodium chloride or in alcohol of different strengths.
