RELATIVE VALUES OF PROTEINS. 



103 



would be smaller the less the difference in the constitution of the two, he used 

 as his standard protein supply either dog flesh or the ground flesh and internal 

 organs (heart, liver, spleen, and testicles) of dogs. This material may be 

 assumed to have supplied the various amino acids, etc., in approximately the 

 proportions required to maintain the protein tissues of the experimental animals 

 with a minimum of loss. With this were compared gliadin and edestin as rep- 

 resentatives of the vegetable proteins differing quite widely from those of the 

 body and casein as an animal protein more or less similar to the tissue proteins. 



The series of experiments on the first dog affords a striking illustration of 

 the difficulties in the way of successful investigation of this question. After 

 fasting for 16 days and receiving only nonnitrogenous feed 1 (sugar and lard) 

 for 28 days more, the daily nitrogen excretion (feces and urine) was reduced 

 to 1.42 grams per day and appeared to have become approximately constant. 

 Quantities of the various protein materials containing this amount of nitrogen 

 were then added in successive periods to the basal nonnitrogenous ration and 

 the effect upon the nitrogen balance determined, the periods covering from 6 

 to 9 days each. In three periods in which dog flesh was fed, the animal 

 gained small amounts of nitrogen (0.08 to 0.17 gram per day) ; in other words, 

 an amount of protein equal to the fasting katabolism sufficed to produce nitro- 

 gen equilibrium. Practically the same result was also attained in the period 

 in which " Nutrose " (a preparation of casein) was fed. Three periods with 

 gliadin, on the contrary, showed in every case a loss of nitrogen ranging from 

 0.33 to 0.52 gram per day ; that is, the gliadin appeared decidedly less valuable 

 than the dog flesh or casein for the maintenance of the body protein. Upon 

 adding more gliadin to the ration it was found necessary to increase the daily 

 amount to the equivalent of about 3.5 grams of nitrogen before nitrogen equilib- 

 rium was reached. 



At the conclusion of this series, however, two 3-day periods on the nitrogen- 

 free ration (preceding and following the period with the larger amount of 

 gliadin) showed that the prolonged feeding on rations poor in protein had so 

 lowered the plane of protein nutrition that the daily fasting katabolism was 

 now equivalent to only 0.95 gram of nitrogen, or on the average of the last 

 two days of each period to only 0.82 gram. In other words, the 1.42 grams of 

 the earlier periods did not represent the absolute minimum on which life 

 could be maintained. A second series of trials was therefore instituted in 

 which dog tissue was compared with casein and edestin. In no case was 

 nitrogen equilibrium quite reached, but the dog flesh still showed a decided 

 advantage over the other forms of protein. The dog, however, had become 

 very much reduced and died during the final period on dog flesh, the autopsy 

 showing an exceedingly anemic condition. The attempt to base the compari- 

 sons of the different proteins upon the absolute minimum of the protein 

 katabolism, in other words, involved such a reduction in the stock of body 

 protein and consequently such an abnormal condition of the animal as to render 

 the value of the results questionable. In succeeding experiments on two other 

 dogs, therefore, the attempt to reach the absolute minimum of the protein 

 katabolism was abandoned and the amounts of the several proteins added to 

 the basal nonnitrogenous ration were either made equivalent to the fasting 

 katabolism in the first period or reduced slightly below it according to the 

 judgment of the experimenter. The results were in accord with those of the 

 first series, the vegetable proteins, gliadin and edestin. proving notably inferior 

 to the dog flesh or the casein. 



1 No mention is made of any supply of ash ingredients other than those contained in 

 the various forms of protein used, with the exception of a small amount of calcium car- 

 bonate (p. 423). 



