564 MECHANISM OF BILE SECRETION. 
it. This was definitely proved by Wertheimer, 1 who injected into the 
circulation of dogs the bile of the ox and sheep. The bile of these 
animals contains a pigment, cholohaematin, which gives a characteristic 
spectrum, and the appearance of this spectrum in the bile of the dog 
showed that cholohaematin had been taken up and excreted. 
Cholesterin. — Whether cholesterin is formed in the liver cells, or in 
the cells lining the bile passages, or in both, is not definitely known. 
In the two cases of fistula of the gall bladder already referred to, the 
presence or absence of cholesterin is not noted. 2 
That the cholesterin is formed somewhere within the liver, and not 
merely excreted by it, is shown by an experiment by Jankau, performed 
in Naunyn's laboratory. 3 He injected cholesterin into dogs, and also 
gave it in their food, and ascertained that it had been absorbed ; but lie 
failed to find any increase of cholesterin in the liver tissue, or in the 
bile. The analyses of the liver and bile made by Kausch 4 in the same 
laboratory show no relationship between the amount of cholesterin in 
the gland, and in its secretion. Thomas, 3 who also worked in Naunyn's 
laboratory, found that there is no relationship between the amount of 
cholesterin excreted and the kind of food taken. When the dog under 
observation suffered from catarrh of the biliary passages, there was a 
marked increase in the cholesterin of the bile. 
From these experiments, and from the fact that cholesterin is always 
found where cells are disintegrating, Xaunyn strongly supports the view 
that cholesterin is produced, not in the liver cells, but from the cells of 
the passages, and that it is a product of the disintegration of their 
protoplasm. 
Lecithin and other compounds of the fatty acids. — The occur- 
rence of these bodies in the secretion from the gall bladder has not 
been observed. On the other hand, lecithin and fat are constant and 
abundant constituents of liver cells. Liver tissue contains about 2 - 35 
per cent, of lecithin, and about 3 or 4 per cent, of fat. 5 Thomas found 6 
that, while cholesterin was unaltered in amount by the administration 
of various diets, the amount of fat in the bile depended largely upon 
the amount of fat taken in the food ; and since the fats of the food are 
frequently stored in the liver cells, it is probable that the fatty acid 
compounds in the bile are derived from this source. 
Influence of Various Factoes upon the Secretion. 
The investigation of the influence of varying conditions upon bile 
secretion is a matter of extreme difficulty, for the bile may accumulate 
in the gall bladder and passages to lie expelled from the liver some time 
after secretion. 
The flow of bile is governed by — 
1. The rate of secretion. 
2. The activity of the muscular walls of the passages. 
3. The pressure upon the liver of adjacent organs. 
1 Arch, de pliysiol. norm, etpath., Paris, 1891, p. 724. 
2 In the colourless fluid from a case of hydrops cystidis fellea?, I found a considerable 
quantity of cholesterin. 
3 "Cholelithiasis," translated by A. E. Garrod, New Syd. Soc, 1896. 
4 Diss., Strassburg, 1891. 
5 Noel Paton, Journ. Physiol., Cambridge and London, 1S96, vol. xix. p. 213. 
6 Loc. cit. 
