PROTEIN. 



163 



nsoluble form from any of its acid solutions 

 b}\the ferrocyanicle and ferridcyanide of potas- 

 sium, which are among the most delicate tests 

 for it ; also, by absolute alcohol, tannin, many 

 of the metallic salts, and by carefully neutral- 

 izing with an alkali. 



Trit oxide of protein. Though protein may 

 be said to be absolutely insoluble in water, 

 it may by prolonged ebullition with ac- 

 cess of air be rendered completely soluble. 

 This is owing to the formation of a soluble 

 oxide of protein, represented by the formula 

 C 40 H 31 N 5 O 15 + HO, containing three 

 additional equivalents of oxygen, and which 

 Mulder has called tritoxide of protein. This 

 interesting compound may be more easily 

 prepared from the chlorite of protein (which I 

 shall presently describe) by the addition of 

 ammonia; the muriate of ammonia which is 

 formed at the same time being afterwards 

 separated by washing with alcohol. 



Tritoxide of protein has, when dry, very 

 much the same appearance as protein ; it is 

 readily soluble in water, nearly insoluble in 

 alcohol, and completely so in ether. It dis- 

 solves in sulphuric and hydrochloric acids and 

 the alkalies, but is precipitated from its solution 

 in water by dilute sulphuric acid, tannin, and 

 several metallic salts, forming compounds with 

 their oxides, having for the most part the 

 formula (C 40 H 31 N 5 O 16 + MO) + (C 40 

 H 31 N 5 O 15 + HO). With nitric acid it 

 behaves like protein, becoming yellow, and 

 forming xanthoproteic acid. Water in which 

 meat has been boiled, as broth, soup, &c., 

 owes its nourishing properties mainly to the 

 tritoxide of protein which is formed during 

 ebullition ; and according to Mulder, both this 

 and the binoxide are formed in meat during the 

 process of roasting. 



Binoxide of protein. The other compound 

 of protein and oxygen just alluded to, called 

 by Mulder the binoxide, consists of C 40 H 3 x 

 N 5 O 14 or the elements of protein plus two 

 equivalents of oxygen. Both this and the tri- 

 toxide exist ready formed in the buffy coat of 

 the blood, which, according to Mulder, con- 

 sists chiefly of these two oxides. Binoxide of 

 protein may be obtained by boiling fibrin in 

 water for many hours, when the protein gra- 

 dually combines with at first two, and even- 

 tually three equivalents of oxygen, becoming 

 successively binoxide, and (if the ebullition is 

 continued long enough) tritoxide; the latter 

 dissolves as it is formed, and may be separated 

 from the insoluble binoxide by washing with 

 water. This process is, however, tedious, and 

 it is more readily obtained from hair, in the 

 following manner. The hair should be freed 

 from grease by washing with ether, and dis- 

 solved in rather a dilute solution of caustic 

 potash, with the aid of a gentle heat, not ex- 

 ceeding 120 or 130. A mixed solution of 

 protein and its binoxide is in this way obtained, 

 from which the protein is first separated by 

 neutralizing the solution with acetic acid, and 

 after filtration the binoxide is precipitated by 

 the further addition of a decided excess of acid. 

 It appears as a yellowish flocculent precipitate, 



and when washed and dried has a dark resin- 

 like appearance. 



Bouchardat obtained a substance by digest- 

 ing moist fibrin in water acidified with one or 

 two-thousandth of its weight of hydrochloric 

 acid, in which it gradually dissolved, which he 

 called albuminose ; it has since been prepared 

 and analysed by Mulder, who considers it to 

 be identical with binoxide of protein; but 

 Liebig, who has recently examined it, says 

 that it cannot be obtained free from sulphur, 

 and consequently that it is not pure binoxide 

 of protein. This oxide is insoluble in water, 

 alcohol, and ether, but dissolves in most of the 

 dilute acids, and in solutions of potash and 

 ammonia ; it is precipitated from its acid solu- 

 tions by ferrocyanide and ferridcyanide of po- 

 tassium, and several other metallic salts. Nitric 

 acid decomposes it, forming xanthoproteic 

 acid, but the yellow colour produced by it is 

 less intense than that obtained with protein. 



These oxides of protein possess considerable 

 physiological interest, from the circumstance 

 that they are contained in the blood, in small 

 quantity during health, but much more abun- 

 dantly in some forms of disease. It is probable 

 that they are formed during every act of respi- 

 ration by the action of the inspired oxygen on 

 the globules or fibrinous matter of the blood ; 

 and Mulder is of opinion that it is through 

 their instrumentality that the atmospheric 

 oxygen is conveyed to the capillaries, there to 

 be employed in effecting the necessary changes 

 in the substance of the body. During fever, 

 when respiration goes on with more than 

 ordinary rapidity, these oxides are formed in 

 much larger quantity ; hence the buffy coat of 

 diseased blood, which was formerly considered 

 to be merely fibrin, consists almost entirely of 

 oxidized protein ; and pus, false membranes, 

 and other morbid products contain it in con- 

 siderable quantity. 



Mulder has recently obtained a third oxide 

 of protein, represented by the formula C 40 

 H 31 N 5 O 20 or protein plus eight equiva- 

 lents of oxygen. As it has not, however, been 

 found to exist naturally in the animal body, it 

 is inferior in point of interest to the other 

 two. Like the tritoxide it is soluble, and is 

 obtained by boiling glutin or yeast for a length 

 of time in water. 



By the action of chemical reagents on pro- 

 tein a multitude of new compounds are formed, 

 most of which have been only imperfectly 

 examined, and indeed possess but little real 

 interest. I will describe a few of the most 

 important. 



Protein and chlorine. When a current of 

 chlorine is passed through a solution of albu- 

 men, or any of the other modifications of pro- 

 tein, a substance is produced, containing C 40 

 H 31 N 5 O 15 Clj, which Mulder considers to 

 be a chlorite of protein, (C 4q H 31 N 6 O 12 + 

 Cl O 3 ). It appears to be formed at the ex- 

 pense of three equivalents of water ; three 

 equivalents of hydrochloric acid and one of 

 chlorous acid being simultaneously produced, 

 the latter uniting with the protein. It sepa- 

 rates as a snow-white flaky precipitate, and 



M 2 



