874 APPENDIX. 



Fremy and Valenciennes 1 have described a series of proteids, viz., ichthin, ichthidin, etc. 

 derived from fish and amphibia. They appear to be either identical with, or closely allied to, 

 vitellin. 



Preparation. Yolk of egg is treated with successive quantities of ether as long 

 as this extracts any yellow coloring matter ; the residue is dissolved in moderately 

 strong (10 per cent. ) sodic chloride solution, and filtered. The filtrate on falling 

 into a large excess of water is precipitated. In this state it is mixed with lecithin 

 and nuclein, and in order to free it from these it was usually treated with alcohol.' 2 

 This, as above stated, entirely changes the vitellin into a coagulated form. It 

 seems probable that the separation of vitellin from the other bodies with which it 

 is mixed in the yolk of egg may be effected by precipitating the sodic chloride 

 solution by the addition of excess of water ; the precipitate is then redissolved in 

 10 per cent, solution of sodic chloride, and the process repeated as rapidly as pos- 

 sible. 



6. Globin. 



Globin, stated by Preyer 3 to be the proteid residue of the complex body haemoglobin (see p. 

 351), ought probably to be considered as an outlying member of this class. It is, however, not 

 readily soluble either in dilute acids or sodic chloride solutions. It is said to be absolutely free 

 from ash. 



CLASS IV. Fibrin. 



Insoluble in water and dilute sodic chloride solutions ; soluble, with difficulty, in 

 dilute acids and alkalies, and more concentrated neutral saline solutions. 



Fibrin, as ordinarily obtained, exhibits a filamentous structure, the component 

 threads possessing an elasticity much greater than that of any other known solid 

 proteid. 



If allowed to form gradually in large masses, the filamentous structure is not so noticeable, and 

 it resembles in this form pure India-rubber. Such lumps of fibrin are capable of being split in 

 any direction, and no definite arrangement of parallel bundles of fibres can be made out. 



At ordinary temperature fibrin is insoluble in water, being dissolved only at very 

 high temperatures, and then undergoing a complete change in its characters. In 

 hydrochloric solutions of 1-5 per cent, fibrin swells up and becomes transparent, 

 but is not dissolved. 4 In this condition the mere removal of the acid by an excess 

 of water, neutralization, or the addition of some salt, causes a return to the 

 original state. If, however, the acid be allowed to act for many days at ordinary 

 temperatures, or for a few hours at 40-60 C., solution takes place, and the result- 

 ing proteid is syntonin. In dilute alkalies and ammonia, fibrin is much more 

 readily soluble, though in this case also the solution is greatly aided by warming ; 

 the resulting fluid contains no longer fibrin, but alkali-albumin. This property is 

 not distinctly characteristic of fibrin, although it dissolves perhaps more readily in 

 both dilute acids and alkalies than do coagulated proteids. None of these solu- 

 tions can be coagulated on heating, which is intelligible when it is remembered 

 that they no longer contain fibrin, but either acid- or alkali-albumin. In addition 

 to the above, fibrin is soluble, though with difficulty and only after a considerable 

 time, in 10 per cent, solutions of sodic chloride, potassic nitrate, or sodic sulphate, 

 the solution being often accompanied by putrefactive changes. These solutions 

 may be coagulated by a temperature of 60 C. , and are precipitated by dilution with 

 water or saturation with solid sodic chloride ; in fact, by the action of the neutral 

 saline solutions the fibrin has become converted into a body exceedingly like myosin 

 or globulin. 5 



On ignition of fibrin a residue of inorganic matter is always obtained ; it is, how- 

 ever, considered that sulphur is the onty one of these elements which enters essen- 

 tially into its composition. In other respects fibrin corresponds entirely in general 

 composition with the other proteids. 



Suspended in water and heated to 70 C., it loses its elasticity and becomes 

 opaque ; it is then indistinguishable from other coagulated proteids. 



1 Compt. Rend., T. xxxviii. pp. 469, 525. 



2 Weyf, op. cit., S. 74. 3 Die Blutkrystalle (1871), S. 166. 



4 Complete solution may, however, take place if the fibrin, as is frequently the case, contains 



any adherent pepsin. 

 6 Gautier, Co: 



rapt. Rend., T. Ixxix. (1874), p. 227. 



