90 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



produced by the decomposition of haemoglobin. Bilirubin is, in fact, 

 identical with the iron-free derivative of haemoglobin called haemat- 

 oidin, which is found in the form of crystals in old blood-clots such 

 as occur in the brain after cerebral haemorrhage (see fig. 24). 



An injection of haemoglobin into the portal vein, or of substances 

 such as water which liberate haemoglobin from the red blood corpuscles, 

 produces an increase of bile pigment. If the spleen takes any part 

 in the elaboration of bile pigment, it does not proceed so far as to 

 liberate haemoglobin from the corpuscles. No free haemoglobin is 

 discoverable in the blood plasma in the splenic vein. 



The amount of bile secreted is differently estimated by different 

 observers ; the amount secreted daily in man appears to vary from 

 500 c.c. to 1 litre (1,000 c.c.). 



THE CONSTITUENTS OF BILE 



The constituents of the bile are the bile salts proper (taurocholate 

 and glycocholate of soda), the bile pigments (bilirubin, biliverdin), a 

 mucinoid substance, small quantities of fats, soaps, cholesterin, 

 lecithin, urea, and mineral salts, of which sodium chloride and the 

 phosphates of iron, calcium, and magnesium are the most im- 

 portant. 



Bile is a yellowish, reddish-brown or green fluid, according to 

 to the relative preponderance of its two chief pigments. It has a 

 musk-like odour, a bitter-sweet taste, and a neutral or faintly alkaline 

 reaction. 



The specific gravity of human bile from the gall bladder is 

 1026 to 1032 ; that from a fistula, 1010 to 1011. The greater con- 

 centration of gall-bladder bile is partly but not wholly explained 

 by the addition to it from the walls of that cavity of the mucinoid 

 material. 



The amount of solids in gall-bladder bile varies from 9 to 14 per 

 cent., in fistula bile from 1-5 to 3 per cent. The following table 

 shows that this low percentage of solids is almost entirely due to want 

 of bile salts. This can be accounted for in the way first suggested 

 by Schiff that there is normally a bile circulation going on in the 

 body ; a large quantity of the bile salts that passes into the intestine 

 is first split up, then reabsorbed and again secreted. Such a 

 circulation would obviously be impossible in cases where all the bile 

 is discharged to the exterior. 



The following table gives some important analyses of human 

 bile : 



