MINERALS IN NUTRITION 25 



each rabbit. In some of the rations, described later, the potassium iodide 

 was combined with salt mixtures as a constant percentage of the ration. 

 In most of the experiments, both the cholesterol and the iodine supple- 

 ments varied directly with the food consumption, the actual amounts 

 eaten being given in the tables. 



The cholesterol content of the rabbits' blood was determined every 

 two or three weeks by the Sackett modification of Bloor's original meth- 

 od. i Autopsies were performed on all rabbits at the end of the experi- 

 ments, and a careful record was made of the degree of damage to the 

 aortas, of liver weights, and of other gross pathologic changes. 



As mentioned earlier, the feeding of 1 percent of cholesterol caused 

 rapid and marked damage to the aortas of rabbits. The excess of choles- 

 terol in the blood developed soon after cholesterol feeding was started, 

 but with considerable individual variation among the rabbits. In general, 

 the damage to the aortas and other arteries was proportional to the dura- 

 tion of the cholesterol excess. Experience Indicated that much of the 

 individual variation might be eliminated if strict attention was given to sex 

 and to litter-mate relationships. It is difficult to obtain large litters of 

 known age and breed and in first-class physical condition, but such selec- 

 tions were made in the subsequent experiments, and the success of the 

 work was dependent on this point. 



Effect of Kelp and of Potassium Iodide 



Chart 1 summarizes the results relating to the protective action of kelp 

 and of potassium iodide on cholesterol-induced atherosclerosis in the rab- 

 bits. Tlie findings are grouped according to ration supplement, with the 

 litters indicated by letters. It is apparent that the kelp supplement tend- 

 ed to reduce the level of blood cholesterol and materially lessened the 

 damage to the aortas. Potassium iodide, on the other hand, caused a 

 significant rise in blood cholesterol and exerted no protective action 

 against damage to aortas. The sex difference which appears in this series 

 of experiments was suggestive of a sex difference in susceptibility to 

 cholesterol injury. Later experiments failed to confirm this finding in 

 every case, although there is still some evidence that males may be slightly 

 less susceptible than females. 



The fact that kelp exerted a protective action, and potassium iodide 

 did not, raised the question as to what the active principle in kelp might 

 be. The high total ash of kelp, plus the predominance of basic elements 

 in the ash, suggested the next line of attack. It seemed possible that 

 the damage to the aortas and other arteries might be related to the acid- 

 base balance of the ration. A salt mixture was prepared containing the 

 basic elements of kelp, and the quantity fed was calculated to provide the 

 basic elements equal to the excess of bases present in kelp. To this was 

 added 30 milligrams of potassium iodide per 100 grams of food. 



Rations containing O.S percent cholesterol — alone, with kelp, and with 

 the salt mixture — were fed to six male rabbits in litter F. The animals 

 receiving the salt mixture developed higher blood cholesterol and more 

 severe damage to arteries than did the animals receiving cholesterol alone, 

 or those receiving cholesterol plus kelp. This led to the discarding of the 

 sex theory as a promising lead for further work. It was apparent that 



'Saokett, G. Modification of Bloor's method for the determination of cholesterol In whole 

 blood 01- blood serum. Jour. Biol. Chem. 64:203-204. 192 5. 



