52 



MANUAL OF HISTOLOGY. 



two right lines, giving rise to deltoid tables (b). Again, two such 



tables very frequently become fused 

 together by their convex sides, or 

 overlap each other (be). We then 

 have the rhombic tables usually 

 ascribed to hsematoidin (fig. 34) ; 

 still showing indentations in most 

 cases at the blunt angle of the rhombs, 

 which gradually become obliterated 

 (dd). It not unfrequently happens 

 that two other crystals become asso- 

 ciated with the two first, so that a 

 four- rayed star is produced (e). These 

 then give origin to four-sided tables 

 on the filling up of the indentations 

 at their corners, and each sometimes 



wig. ss.-very lar^e crystals of hemauddin assumes eventually the appearance of 



from the ovary of a cow, obtained by treat- an oblique dice, from its having 



gradually become thickened (fg.) 



36. 

 Uro'erythrin, or Uroheematin. 



-jln the urine a very small quantity of a red colouring matter is to be 

 found, which gives to the fluid its yellow tint, and may colour the 

 sediment of the same of a lively red. This substance is very unstable, 

 and only obtainable with great difficulty, whence our imperfect acquaint- 

 ance with its nature. The colouring matters of urine were first investigated 

 by Scherer, and more recently by Harley. The latter obtained a red 

 pigment almost insoluble in water, but freely so in warm fresh urine, 

 giving to the latter a yellow tint, and to ether and alcohol, in which it is 

 also dissolved, a beauteous red colour. Harley found this pigment to be 

 ferruginous, and regards it as a species of modified hsematin. Besides 

 this, some other pigmentary matters were also met with by him. 



A red pigment has been recently discovered by Jaffe in the urine, 

 possessed of some spectroscopic peculiarities : it has been named by him 

 urobilin, from the fact of its also occurring in bile and the excrements. 



Blue and violet colouring matters, which may occasionally be met with 

 in human urine, appear in but very small quantity. Under certain 

 circumstances indigo has been observed here without having been taken 

 up from without (Sich&rer), while indikan, C 26 H 31 N0 17 , or chromogen of 

 indigo is, according to Hoppe, constantly present. 



Black Pigment, or Melanin. 



Black pigment is found in normal tissues in the form of very minute 

 granules or molecules. It is a substance remarkable for its insolubility 

 and unchangeableness. Melanin . is not soluble either in water, alcohol, 

 ether, dilute mineral acids, or concentrated acetic acid. It is dissolved in 

 warm potash solutions, but only after some considerable time. The same 

 takes place in concentrated nitric acid, by which the melanin is decom- 

 pounded, however. Its ash contains iron. 



The investigations in regard to the constitution of melanin which have 



