948 THE EXTERNAL SECRETIONS 



cholic acid radicle of the latter, which unites in some way with the cholesterol and 

 keeps it in solution. Little is known regarding the origin of this substance. It 

 may be derived from the food or from the cholesterol of the destroyed red blood 

 corpuscles. Regarding its place of origin, Naunyn makes the assertion that it is 

 eliminated chiefly by the lining cells of the gall-bladder, this statement being based 

 upon the fact that the bile of the latter contains a larger amount of cholesterol than 

 that of the hepatic duct. But since the relative richness of the bladder-bile in 

 this substance may be due to the fact that the cholesterol here secreted is not so 

 easily converted into bile salts, the preceding deduction may not be correct. A 

 disturbance of these oxidations in consequence of traumatism and inflammation 

 of the wall of the bladder, or in consequence of general metabolic disorders (meno- 

 pause), frequently leads to the formation of gall-stones which may at times occupy 

 every recess of the bladder and also find their way into the large biliary channels. 

 The constant irritation set up by these concretions tends to excite contractions 

 of the bladder, which in the course of time mold these masses into many-sided 

 fragments possessing sharp points and sides. As has just been stated, the chief 

 constituent of these concretions is cholesterol (20 to 90 per cent.) to which some 

 desquamated epithelium has been added. ^ 



The phospholipins of bile present themselves principally in the form of lecithin. 

 Practically nothing is known regarding their origin and function. In human bile 

 the lecithin, obtained from the alcohol-soluble material, amounts to 1.7 per cent., 

 but varies considerably in accordance with the character of the food ingested. 

 This fact might lead us to suspect that it is derived from the constituents of the 

 diet, but it may also be true that it originates from the destroyed red blood cor- 

 puscles. 



The peculiar color of the bile of the carnivora is due to certain pigments of which 

 bilirubin is the most important. This substance is unstable and is easily oxidized 

 into a green pigment, known, as biliverdin, which in turn gives rise to a whole series 

 of bodies, such as the blue biUcyanin. On further reduction it is converted into 

 urobilin, one of the coloring materials of urine. In the herbivora the chief pigment 

 is biliverdin, but it seems that the aforesaid pigments are interchangeable. Bili- 

 ruhin (C32H36N2O6) is an iron-free compound and is derived from the hemoglobin 

 of the red corpuscles. Consequently, its formation must be dependent upon the 

 rate of destruction of these cells. Since the bile contains only a trace of iron, it may 

 be surmised that this element is stored in the liver cells to be made use of sub- 

 sequently in the formation of new hemoglobin. Bilirubin is prepared from 

 powdered red gall-stones by dissolving the chalk with hydrochloric acid and extract- 

 ing the residue successively with chloroform. The pigment crystalUzes from this 

 solution in beautiful rhombic tables or prisms. Biliverdin (C32H36N4O8) is an 

 amorphous iron-free body. It may be formed from bilirubin by oxidation and may 

 be reconverted into this pigment by putrefaction or by the addition of ammonium 

 sulphid. By reduction with sodium amalgam it is changed into hydrobilirubin, 

 a substance identical with stereobilin. Similar reductions go on when the bile 

 pigments reach the intestine, so that they are not recognizable as such in the feces 

 or urine. The most important derivative of bilirubin is stercorubin or urobilin. 

 To this body is due the brown color of the feces. In urine it appears as urobiligen, 

 a colorless substance which is changed into urobilin under the influence of the oxy- 

 gen of the air. When the bile is prevented from entering the intestine, the urine 

 does not contain this substance. 



The Intestinal Glands. — The mucous membrane of the small 

 intestine contains numerous goblet cells, similar in structure to those 

 previously noted in the mucosa of the stomach. Their function is to 

 discharge mucus which serves to lubricate the surfaces of the intestine 



1 Kramer, Jour, of Exp. Med., ix, 1907;Lichtwitz, Arch. klin. Med., xcii,1907, 

 100, and Bacmeister, Munch, med. Wochenschr.,1908. 



