104 



MAINTENANCE RATIONS OF FARM ANIMALS. 



Upon two points, however, Michaud's results seem open to question. 



First, the pure proteins which he employed, as well as the sugar and lard, 

 can have contained but minimal amounts of ash, while, as already stated, no 

 mention is made of the addition of any ash ingredients except calcium car- 

 bonate. In those periods, then, the animal was apparently in a state of par- 

 rial or entire mineral hunger. The dog flesh (or in two periods horse flesh), 

 on the other hand, contained its normal amount of ash, and it is not im- 

 possible that this was an important factor in determining its higher value, 

 although it must be admitted that this explanation does not apply to the 

 casein periods. Second, dog tissue or horse flesh is by no means pure protein, 

 but in addition to ash constituents contains a great variety of organic com- 

 pounds, which may have been quite as important as the protein. In other 

 words, the periods on tissue are not comparable with those on pure proteins. 



zisterer's experiments. 



Zisterer 1 has reported two series of similar experiments, also on a dog. 

 They differed from Michaud's, however, in that the periods were shorter and 

 that each feeding period was interpolated between two periods on a nonnitro- 

 genous basal ration from the average results of which the fasting protein 

 katabolism of the animal for that particular bodily condition was computed. 

 Zisterer experimented with casein, wheat gluten, and lean meat extracted 

 with water (muscle protein). He added to his rations the chlorids of sodium, 

 potassium, and calcium, but no other ash ingredients. The ash content of 

 the feeds was small. The energy supply in the feed was in every instance 

 ample to supply the needs of the animal as computed according to E. Voit. 2 

 Taking the first period, on casein, as an example, the preliminary period on 

 nitrogen-free feed covered five days and the one following the feeding period 

 four days. On the average of the last two days of these periods, the fasting 

 protein katabolism was equivalent to 1.975 grams nitrogen daily. During the 

 intermediate 4-day period, casein containing 2.018 grams nitrogen per day 

 was fed and the average daily nitrogen excretion for the last two days was 

 found to be 2.333 grams. Two series of trials of this sort, made in inverse 

 order, yielded the following results: 



Protein metabolism of a dog — Zisterer. 





Fasting 

 nitrogen 

 katabolism. 



Feed 

 nitrogen. 



Total 

 nitrogen 

 excretion. 



Gain of 

 nitrogen 

 by animal. 



Series I: 



Grams. 



Grams. 



Grams. 



Grams. 





1.975 



2. 018 



2. 333 



-0.315 





2.125 



2.021 



2.316 



- .294 



Wheat gluten 



1.951 



2.017 



2.113 



- .096 



Series II: 











Wheat gluten 



1.800 



2.111 



2.276 



- .1C5 



Muscle protein 



1.806 



2.110 



1.903 



+ .207 



Casein 



1.708 



2.108 



2.050 



+ .058 



Average: 











Casein 



1.842 



2.063 



2.192 



- .129 



Muscle protein 



1.966 



2. 066 



2.109 



+ .043 



Wheat gluten 



1.876 



2.064 



2. 195 



+ .131 



If we represent the total nitrogen excretion upon the muscle protein by 100, 

 That observed with the other proteins was as follows: 



1 Zoitschrift fur Biologie, vol. 53, p. 157. 



- Ibid., vol. 41, p. 113. 



