PROTEINS IN THE DIET MITCHELL. 225 



Folin's theory, the endogenous catabolism. Thomas has given to 

 meat, milk, and fish, values approximating 100, indicating complete 

 utilization of the absorbed nitrogen. On the other hand, to the pro- 

 teins of corn and wheat have been given values of 30 and 40, 

 respectively, while the proteins of rice, potatoes, and peas are graded 

 88, 79, and 56, in order. Thus, according to Thomas, animal proteins 

 are two to three times more valuable in adult nutrition than the 

 cereal proteins. Attempts to confirm Thomas' results have not been 

 particularly successful, and several flaws can be found in the plan- 

 ning of his experiments and in his method of selecting some results 

 and discarding others in computing average biological values. The 

 selection of some experimental results in preference to others is al- 

 ways a hazardous undertaking. 



More recent determinations of the biological values of proteins 

 have in general indicated smaller differences between animal and 

 vegetable proteins than those shown by the results of Thomas. Mar- 

 tin and Robison (5) in a recent report have given to wheat proteins 

 a value of 35 and to milk proteins a value of only 51. In analogous 

 experiments on pigs, McCollum (6) has found that at low levels of 

 intake the nitrogen of corn, oats, and wheat seemed to be entirely 

 utilized in the processes of repair. In later experiments (7) on 

 growing pigs at higher levels of intake, results were obtained which, 

 when recalculated according to the method of Thomas, give values 

 of 42 to 48 for the proteins of corn, oats, and wheat, a value of 67 

 for casein, and a value of 80 for the proteins of milk. Thus, ac- 

 cording to these values, the cereal proteins do not seem to be so 

 greatly inferior to milk proteins, even in growing animals, as the 

 values of Thomas would indicate. The evidence obtained by Sher- 

 man (8) in his experiments on the efficiency of diets consisting 

 essentially of wheat bread or of corn meal or oatmeal supplemented 

 by only small amounts of milk, also indicate a higher value for these 

 proteins in adult nutrition than have generally been assigned to them. 



The work of Osborne and Mendel (9), using an entirely different 

 method, also assigns to the cereal proteins values much nearer those 

 of animal proteins than the work of Thomas. In work on growing 

 rats, using rations complete in every respect except for the protein 

 contained in them, they have expressed the relative values for growth 

 of the proteins tested as the increase in weight (in a four or eight 

 week period) per gram of protein consumed. For the proteins of 

 barley, rye, oats, and wheat, average values of 1.4 to 1.9 grams of 

 gain per gram of protein consumed were obtained. These values 

 may be compared with values of 2.3 and 1.7 obtained for lactalbumin 

 and casein, respectively, in eight-week feeding periods with rats of 



