RELATIVE VALUES OF PEOTEINS. 



107 



July and two in September to November of the same year. He determined, bis 

 protein katabolism upon a nonnitrogenous diet (chiefly carbohydrates) in three 

 or four day periods in each series and also interpolated single nitrogen-free 

 days during each series. The results of these periods were more or less vari- 

 able, but the final values employed by him, although representing to some de- 

 gree an arbitrary selection of days, seem, on the whole, to fairly represent the 

 nitrogen katabolism ; that is, they satisfy the second of the two conditions 

 above pointed out. 



With these values for the protein katabolism were compared the nitrogen 

 balances of periods of from two to four days (or in a few cases only one day) 

 in which single foods were consumed along with sufficient carbohydrates and 

 fat to fully supply the demands of the body for energy. The technic of these 

 periods, however, can hardly be regarded as entirely satisfactory. Out of 33 

 days, the results of which are contained in his final table, the protein digested 

 was greater than the average protein katabolism on the nitrogen-free days in 

 21 cases, the difference sometimes being considerable and sometimes relatively 

 insignificant. As already pointed out, this tended to make the availability 

 appear too low, and it is noteworthy that the excess of food protein is especially 

 large in the experiments upon wheat flour which show a strikingly low avail- 

 ability. On the other hand, however, it is also true that a very low availability 

 was found for maize protein in experiments in which but a slight excess was 

 fed. In these experiments, however, the apparent digestibility of the protein 

 was remarkably low, ranging from 56 to 69 per cent, but a similar low digesti- 

 bility (about 68 per cent) was found in the trials with rice. Furthermore, the 

 periods were relatively short and in many instances the nitrogen intake varied 

 considerably within the period, so that it may be questioned whether the nitro- 

 gen excretion reached a stable value. Moreover, to some extent there was a 

 more or less arbitrary selection of days to be compared. For all these reasons 

 Thomas's results must be accepted with more or less reserve. 



His final results for the percentage availability of the protein of different 

 materials are as follows, the results being calculated in three different 

 ways, viz : 



A. Fecal nitrogen all regarded as derived from the food, that is, the compari- 

 son is made upon the basis of the apparently digested protein. 



B. Fecal nitrogen regarded as being all present in the form of metabolic 

 products. 



C. One gram of fecal nitrogen is regarded as derived from metabolic products 

 and the remainder from undigested food. 



Relative availability of proteins — Thomas. 





1 



A. B. 



! 



C. 



Lean beef 



/ 104.94 

 \ 106.51 



99. 65 

 f 103. 09 

 \ 85. 73 

 { 88. 17 

 / 83.00 

 \ 86. 26 

 ( 72. 60 

 \ 73. 38 

 / 56.63 

 \ 53. 40 



66.69 



63.45 

 { 29. 17 



36. 70 

 \ 64. 50 



41. 35 

 { 27. 74 



103. 75 

 L05. 73 

 99. 71 

 L02. 06 

 89.37 

 91.95 

 88. 53 

 90. 73 

 78. 85 

 79.45 

 73.48 

 70. 35 

 70. 14 

 69. 02 

 36. 25 

 43.04 

 42.04 

 51.10 

 39. 75 





Milk 





Fish 





Rice 



87.09 

 89.55 



Crabs 



Yeast 



69. 58 

 71.45 

 67. 12 



Casein 



Nutrose 









48. 97 



36. 94 



