Curt P. Richter 503 



6. Diets self-selected from purified or nearly purified substances are more 

 efficient than regular synthetic stock diets or diets composed of natural foods. 

 Rats which selected their diets from sucrose, olive oil, casein, five mineral 

 solutions, cod liver oil, and yeast ate approximately 35 per cent less food per 

 day as measured in grams, than rats of the same age and weight on the stock 

 diet. However, owing to the higher fat content of the self-selection diet, the 

 caloric intake on the latter was only 18.7 per cent less than that of the animals 

 on the stock food (Richter, Holt and Barelare"). Experiments on dietary selec- 

 tions of pregnant and lactating rats offered the same choice of substances gave 

 the most striking evidence for the efficiency of the self-selected diets. They 

 showed a greatly increased appetite for protein (casein), fat (olive oil), calcium 

 and phosphorus. At the height of lactation, rats on the self-selection diet nurs- 

 ing the same number of young ingested only about half as much food as meas- 

 ured in grams as rats on the stock diet. Despite the much lower food intake, the 

 mother and young remained in excellent shape and the young were normal in 

 size. Presumably the lowered food intake of the rats on self-selection diets is 

 directly due to the ability to obtain the needed calcium, phosphorus, etc., with- 

 out being forced to take increased amounts of the other unneeded components 

 of the mixed diet (Richter and Barelare"). 



7. Rats deprived of endocrine secretions luhich regulate metabolism of car- 

 bohydrates, fats, proteins, or electrolytes, will when given the opportunity, 

 select substances which compensate for the loss of the secretions. Thus, adre- 

 nalectomized rats compensate for the increased excretion of sodium by in- 

 gesting large amounts of sodium solutions and as a result keep themselves alive 

 and free from symptoms of insufficiency. Likewise, parathyroidectomized rats 

 manifest a greatly increased appetite for solutions of calcium, or for the closely 

 related metals, magnesium and strontium (Richter and Eckert"). By virtue of 

 the increased intake of these metals they not only survive but remain free from 

 symptoms of tetany. Rats made diabetic by removal of the pancreas select 

 substances, chiefly fat, which help to alleviate or even eliminate diabetic symp- 

 toms. They actually gain weight, lose their polydipsia, polyphagia, and hyper- 

 glycemia (Richter and Schmidt^). 



8. The self-selection activities of rats may be used to determine functions of 

 various glands and may serve to short-circuit prolonged biochemical investiga- 

 tion. For example, it took biochemists many decades to determine that the 

 adrenal glands play an important part in the regulation of sodium metabolism. 

 Endless studies of the mineral content of the blood, urine, and feces were made 

 before this result was achieved. With the self-selection technique, by offering 

 adrenalectomized rats access to a variety of substances in purified form, we 

 could have determined within a few days, and long before the advent of mod- 

 ern biochemical methods, that the adrenal glands are concerned with the 

 regulation of sodium metabolism. In the same way we could have determined 

 that the parathyroids are concerned with the regulation of calcium metabo- 

 lism. Thus far this method has indicated that riboflavin is concerned with the 



