48 THE ALBUMINS. 



The skeleiins are in part related to elastin and partly to collagen. 

 Spongin and conchiolin thus do not give Millon's reaction, and 

 accordingly yield no tyrosin on decomposition, while both are 

 obtained from fibroin, kornein, and elastoidin. It appears, on the 

 other hand, that, with the possible exception of kornein, all the 

 skeletins contain no sulphur. 



The amyloid substance, finally, occupies a unique position among 

 the albuminoids. It is apparently met with only under pathologic 

 conditions, and is then found in the connective tissues. Like the 

 true albumins, it consists of carbon, hydrogen, nitrogen, oxygen, 

 and sulphur, and on decomposition yields both leucin and tyrosin. 

 It gives Millon's reaction, that of Adamkiewicz, and the xantho- 

 proteic reaction. It is insoluble in water, alcohol, ether, dilute 

 hydrochloric acid, and acetic acid. Concentrated hydrochloric acid 

 and solutions of the alkaline hydrates cause its solution, but at the 

 same time transform it into acid albumin or alkaline albuminate. 

 The gastric juice, contrary to what has been claimed, likewise causes 

 the substance to dissolve. Most characteristic is its behavior toward 

 iodine and aniline green. The latter is colored red. Dilute aqueous 

 solutions of iodine color the substance a brownish red or a bluish 

 violet, which passes into blue on treating with sulphuric acid. lodo- 

 methyl aniline stains the substance red, especially after previous 

 treatment with acetic acid. 



The more important members of the various groups which have 

 been briefly considered in the preceding pages, their specific proper- 

 ties, and methods of isolation, will be dealt with in greater detail in 

 connection with the tissues in which they are principally encountered. 

 The derived albumins also, which are now to occupy our attention, 

 are likewise considered only in a general way at this place, as we 

 shall have opportunity to study them in greater detail in the 

 chapters on the Blood and Digestion. 



THE DERIVED ALBUMINS. 



Fibrin. Fibrin occupies a unique position among the albumins. 

 So far as its general chemical composition goes, it is unquestionably 

 closely related to the albumins proper. It contains carbon, hydro- 

 gen, nitrogen, oxygen, and sulphur in very much the same propor- 

 tion as the true' albumins, and, like these, yields leucin, tyrosin, 

 glutaminic acid, asparaginic acid, and glycocoll on decomposition. 

 On the other hand, fibrin is insoluble in the common solvents of the 

 true albumins, viz., in water and neutral saline solutions. Acids and 

 alkalies cause its dissolution, but during this process the substance 

 itself is transformed into acid albumin or alkaline albnminate, as 

 the case may be. In this respect fibrin is closely related to the 

 coagulated albumins. It further merits a place among the derived 

 albumins, however, by reason of its being itself a derivative of a true 

 albumin, namely, fibrinogen, which is transformed into fibrin through 



