1909.] Destiny of Cholesterol in the Animal Organism. 513 



others, which had previously been fed in an ordinary way and led the 

 ordinary domestic life, yielded a mixture of cholesterol and coprosterol. The 

 animals fed on the artificial and vegetable diets gave no coprosterol. This 

 recalls the experiences of Muller,* who found that in man a prolonged milk 

 diet resulted in the excretion of cholesterol and not coprosterol. In all our 

 experiments on meat diets the total cholesterol and coprosterol excreted was 

 considerably less than that taken in with the food. Without considering the 

 cholesterol poured into the gut with the bile, the percentage loss in 

 Experiments 1 and II together was 53 per cent. ; in Experiment III, 40 per 

 cent. ; and in Experiment IV, between 59 and 60 per cent., an average loss of 

 - 08 gramme per day. Two alternative explanations of these results suggest 

 themselves. 



(1) The hypothesis put forward in an earlier paperf that cholesterol is a 

 substance which is strictly conserved in the animal economy : that when the 

 destruction of the red blood corpuscles and possibly other cells takes place in 

 the liver, their cholesterol is excreted in the bile, and that the cholesterol of 

 the bile is reabsorbed in the intestine along with the bile salts, and finds its 

 way into the blood stream to be used in cell-anabolism ; and further, that any 

 waste of cholesterol might be made up from that taken in with the food. 

 This latter process would of course be limited in man and carnivorous animals 

 by the change of cholesterol into coprosterol, and in herbivorous animals by 

 the fact that their normal food does not contain cholesterol, but isomeric 

 substances such as phytosterol, which would have to be converted into 

 cholesterol before utilisation. Further evidence in support of this hypothesis 

 in the case of herbivorous animals was brought forward by Miss Eraser' and 

 one of us in a paperj on the " Inhibitory Action of the Sera of Rabbits fed on 

 Diets containing varying Amounts of Cholesterol on the Haemolysis of Blood 

 by Saponin." 



(2) The change of cholesterol into coprosterol is generally supposed to be 

 one of simple reduction brought about in the intestine by the bacteria of 

 putrefaction. We have, however, no experimental evidence that coprosterol 

 is a simple reduction product of cholesterol, as it is quite different from any 

 of the bihydrocholesterol derivatives hitherto produced in the laboratory ; and 

 further, attempts to bring about the change in vitro by means of bacteria 

 have so far been unsuccessful. Whatever the exact nature of the change 



* " Reduction of Cholesterol to Coprosterol in the Human Intestine/' ' Zeit. physiol. 

 Chem.,' 1900, vol. 29, pp. 129—135. 



t " Origin and Destiny of Cholesterol," Part III, ' Roy. Soc. Proc.,' B, vol. 81, 1909, 

 p. 109. 



% "Origin and Destiny of Cholesterol," Part V, 'Roy. Soc. Proc., : B, vol. 81, 1909, 

 pp. 230—247. 



