1908.] Destiny of Cholesterol in the Animal Organism. Ill 



in the food taken. In experiments in which cholesterol free food was given 

 no cholesterol was found ; thus a dog fed for 31 days on oatmeal and water 

 passed no more than - l gramme of impure cholesterol in the faeces. 



From these observations we were led to the conclusion that the cholesterol 

 of the bile must either be destroyed, or absorbed, along with the bile salts in 

 the intestine, and taken into the blood stream. 



The latter hypothesis is more in accordance with the great stability of the 

 cholesterol molecule, and is supported by the observation of Pribram* that 

 emulsions of cholesterol with olive oil, when injected into the stomach of the 

 rabbit, cause an increase in the cholesterol content of the blood. 



From a consideration of these facts we have been led to put forward with 

 regard to the origin and destiny of cholesterol the following working 

 hypothesis : — 



1. Cholesterol is a constant constituent of all cells, and when these cells 

 are broken down in the life process the cholesterol is not excreted as a waste 

 product, but is utilised in the formation of new cells. 



2. A function of the liver is to break down dead cells, e.g., blood corpuscles, 

 and to eliminate their cholesterol in the bile. 



3. After the bile has been poured into the intestine in the process of 

 digestion the cholesterol is reabsorbed, probably in the form of esters, along 

 with the bile salts, and carried by the blood to the various centres and 

 tissues for re-incorporation into the constitution of new cells. 



The question arises whether the excretion and subsequent absorption of 

 the cholesterol of the body form a regular and exact cycle, or whether there 

 is any wastage of cholesterol which would require to be made up by the 

 animal either by actual synthesis in the body from simpler substances or by 

 the utilisation of that taken in the food. With reference to the wastage of 

 cholesterol it must be pointed out that not inconsiderable quantities are 

 excreted through the skin ; the sweat and sebum of men have been shown 

 to contain cholesterol, and in the case of the sheep the sweat, being absorbed 

 by the wool, enables us to demonstrate the presence of large quantities of 

 cholesterol and isocholesterol. How is the wastage made up ? Considering 

 the remarkable chemical nature of cholesterol it would appear less probable 

 that it is synthesised by the animal than that the loss is made up by the 

 absorption of cholesterol obtained from the food. In the case of carnivora 

 the cholesterol is contained in their food as such, and might easily be 

 utilised. On the other hand, the food of the herbivora contains no 

 cholesterol, but instead the closely related phytosterols, and the question 

 arises whether this closely allied substance can be utilised by the animal. 

 * 'Bioch. Zeit.,' 1906, vol. 1, p. 413. 



