50 MANUAL OF HISTOLOGY. 



putrefying bile we meet with Na 2 S0 4 . The circumstance that most 

 of the bile poured out into the intestine is reabsorbed, as observed by 

 Bidder and Schmidt, thus explains, at least partially, the origin of the 

 sulphates, which eventually leave the body with the urine. 



Cystin, C 3 H 7 NS0 2 . 



This substance is remarkable for the large quantity of sulphur which 

 it contains, amounting to over 26*5 per cent. 



Cystin crystallizes in colourless hexagonal tables 



II or prisms (fig. 32), and is insoluble in water, 

 alcohol, and carbonate of ammonium. It is, on 

 1JJ the other hand, readily soluble in mineral acids 



r ->. and in alkalies, from which it may be precipitated 



r xv by organic acids, as, for instance, by acetic acid. 



/ v T 1 ^c-^V. Cystin enters into combination with both acids 

 \-/ VS^3 an d alkalies. Its mutation products and consti- 

 ^^ tution have not as yet been ascertained, nor do 

 32,-Crystais of cystm. we ^ QW in ^^ form gul p hur is con tained in it. 



Cystin is of rare occurrence ; it forms certain kinds of urinary calculi, 

 and may also appear as an abnormal constituent of urine. 



It was once met with in the liver (Sclierer) ; likewise in the tissue of 

 the kidneys of oxen by Cloetta, but not invariably. The physiological 

 relations of the substance are still quite obscure. 



I. Animal Colouring-Matters. 



35. 



The animal colouring-matters, which are not found in the vegetable 

 kingdom, have their origin for the most part from the natural pigment of 

 the blood, haemoglobin ( 13). They are met with either as artificial 

 decomposition products, or occur in the living body. 

 Haematin, C 34 H 34 N 4 Fe0 5 (Hoppe). 



This substance, as already mentioned, may be obtained from the red 

 blood-corpuscles or hsemoglobulin, but only in a coagulated form. 



According to Hoppe, haematin usually presents itself as an amorphous 

 blue-black substance, which becomes of a reddish-brown on being triturated. 

 It is insoluble in water and alcohol, but soluble in the latter if there be 

 added to it a certain small amount of sulphuric or nitric acid. It may 

 likewise be dissolved in a watery or spirituous solution of ammonia ; 

 and also in caustic alkalies in dilute watery or alcoholic solution. Such 

 a fluid containing hsematin is frequently changed to a greenish colour 

 by the action of a large amount of potash especially if it be boiled. 

 Haematin, suspended in water, is decolorised by the action of chlorine 

 with the formation of chloride of iron ; the dried powder also becomes 

 green by contact with chlorine gas. Dichroism is seen in alkaline, but 

 not acid solutions of haematin ; in a thin layer they appear olive-green, 

 in a thick stratum red (Lfrucke). 



With the aid of concentrated sulphuric acid, the iron it contains 

 may be extracted from haematin, water taking its place in the com- 

 bination (Hoppe). 



Hydrochlorate of Haematin, Hsexnin, C 34 H 34 N 4 Fe0 5 . HC1 (Hoppe). 

 We are indebted to Teiclimann for our acquaintance with this peculiar 



