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* PROTECTIVE COLORATION. 467 PROTEINS. Africau Insects," Traiisuctioiis Entomologicul Society of London, 1S92 ; Fischer, "Weitere Unteisuchungen iiber die Vererbung erwor- bener Eigenschaften," Allgemeine Zeitschrift fiir Entomologie, vol. vii. (1892); Piepers, Mimicry, iieleiction, Darwinismus (Leyden, 1903) ; with the writings of Weismann. Trimen, Cope, Meldola, Haase, Von Linden, Sokolowsky, Port- chinsky, Riley. Weir. .Semper, Von Wattenwyl, Schroder. Butler. Distant, Zenneek. Werner, Eschericli. Peckham, Hickson, Herdman. PROTECTOR. An English title equivalent to that of regent, denoting a non-regal head of the Government under exceptional circumstances, as during a minority or an interregnum. The title was given to Humphrey, Duke of Gloucester, dur- ing the minority of Henry VI. from 1422 until the crowning of the young King in 1430. Richard, Duke of York, father of Edward IV. and Richard III., acted as Protector of the Kingdom at dift'er- ent times during the later years of Henry VI. 's reign. His son. Richard, Duke of Gloucester, was Protector for about two months in 1483. prior to his accession in the same year as Richard III. The Duke of Somerset, at the head of a council during the minority of Edward VI., bore the title from 1547 to 1549. until he was deposed by his colleagues. In 1053 Cromwell was installed as Lord Protector of the Commonwealth of England, Scotland, and Ireland under the provisions of the Instrument, of Government (q.v.), and in 1657 was reinstalled under the provisions of the Hum- ble Petition and Advice. On his death, in 1(J5S, his oldest son. Richard, succeeded to the title and authority, but resigned the office in the following year. PROTECTORATE. A relation assumed by a stronger nation toward a weaker one whereby the former protects the latter from hostile in- vasion or dictation and interferes more or less in its interjial affairs. This relation is estab- lished by treaty between the protecting and the protected State, or among a nun)ber of States in respect to another State, by which the extent and character of the protectorate are determined. Usually the foreign relations of the protected State, including the right to wage war. are eon- trolled by the protecting State. Examples of ex- isting protectorates are Tunis, under French protection, and North Borneo. Bechuanaland, Sonialiland. British Central Africa, and British East Africa, under British protection. PROTEIDS. See Proteixs. PROTEINS (from Gk. irpQros, protos, first). A name applied to an exceedingly important group of chemical substances, occurring abun- dantly in the organisms of animals and plants. The principal component elements of the pro- teins are carbon, hydrogen, oxygen, and nitrogen. When burned, however, the proteins generally leave behind a certain amount of mineral matter, and it is as yet unknown whether such mineral constituents form with the organic portion of the proteins true chemical compounds, or merely physical mixtures. The classification of the pro- teins is based, not on their chemical constitution, as in the case of most oth»r groups of carbon compounds, but on a knowledge of some of their physical properties and of their behavior toward certain reagents. Such a classification is from a scientific point of view very imperfect, and so it must remain until light shall be thrown upon the arrangement of the atoms within their molccules- This,^ however, is a very difficult problem. In the first place, the proteins are as a rule quite unstable and are strongly affected by ordinary chemical reagents and by relatively slight changes in the physical conditions. 'Further, any one familiar with the methods of determin- ing the constitutional formula of an organic com- pound (see Carbon Compolxds) will readily see the difficulty of ascertaining the constitution of a compound, for instance, like the oxyh;pnioglobin of horses' blood, whose molecular formula is, according to Hufner, Cj5;H5KXi„SjFeO„„.28H,0. Yet this is a crystalline compound, and so it is probable that it has been isolated. In the case of amorphous substances, as most proteins are, even this often remains uncertain, and then our knowledge is from the point of view of the theo- retical ciiemist very imperfect indeed. It must also be remembered that the protein substances as they exist in the organism of a living animal or plant are probably more or less different from what they are when examined in the test-tube of a chemist. What the difference consists in is not known, for we are entirely ignorant of the nature and character of living matter. And so all statements concerning the proteins refer to dead protein alone. In discussions of the food and nutrition of maa and animals the term 'protein' is commonly ap- plied to the total nitrogenous material present in the food or feeding stuffs of animal and vege- table origin, and includes a number of different groups of compounds with correspondingly differ- ent nutritive values. The group in its relation to nutrition is commonlv subdivided as follows; Proteids I .^.Ibuminoids. I CoUagens or gelatinoids. ' I Aroido-acids, etc. The albuminoids, sometimes called 'true pro- teids,' which include albumin, globulin, etc.. are the most important of the nitrogenous constitu- ents of foods, examples being the albumin of milk and eggs, the casein of milk, myosin of meat, gluten of wheat, etc. The gelatinoids are mostly of animal origin and include collagen, gelatin, elastin, keratin, etc., bodies which are characteristic of connective tissues as tendons, ligaments, horns, etc. Distinguished from the above are the non-proteids, which include the kreatin, kreatinin, and other extractives of meat, and the amides, amido-acids, etc., of vegetable foods. In general the protein of animal foods and cereal grains is very largely composed of proteids, especially those designated above as albuminoids or true proteids. The true proteids can be trans- formed into nitrogenous body material and thus go to form the blood, muscle, tendon, nerve, etc., of the animal body. They are also sources of energy-. Gelatinoids, svich as gelatin, when burned in the body, yield energj-, but cannot go to form nitrogenous tissue. Like carbohydrates and fat, gelatinoids undoubtedly protect protein from cleavage. The non-proteids, though useful to give flavor, etc., appear to have but little nutritive value except in so far as they serve as fuel for the body. It may be that some of them have an especial use as sparcrs of protein. Thus it has been suggested that asparagin may serve as a nitrogenous nutrient in the place of proteids for