Morgulis. — Studies on Fish Nutrition 43 



feeding was resumed. That the retention was purely temporary- 

 is seen from the fact that within the next few days the elimination 

 was abnormally high, especially between the sixth and ninth day 

 when it became actually 30.8 per cent more than the nitrogen 

 contained in the food for that period. This delayed elimination 

 of nitrogenous waste points to the possibility that the excretory 

 mechanism of the trout suffered an injury in consequence of 

 starvation, which it required several days, when food was given, 

 to restore to normal functioning. 



The similarity of the results obtained in these three exper- 

 iments is very striking, those of 000.5 and 000.7 being practically 

 identical. 



The dry feces formed a much greater per cent of the dry 

 matter consumed with the food, than in any of the previous 

 experiments (9.95 per cent). The utilization of the protein during 

 the entire fifteen day period is 94.4 per cent, which compares very 

 favorably with the extent of utilization observed in the other 

 experiments. The utilization of the fat which has been reduced 

 to only 83.8 per cent demonstrates once more, and more poignantly 

 than in any of the previous experiments, the particularly dele- 

 terious influence of fasting upon fat utilization. The reason for 

 this must unquestionably be looked for in the longer duration of 

 the fast. To explain these facts it may be necessary to assume 

 that a more lasting damage was done to the glandular structures 

 of the animal, the pancreas and the liver, which lead to a defective 

 digestion and absorption of fats. Further investigation of this 

 question would at any rate be desirable. 



In spite of the low degree of utilization of the food materials, 

 the "Index of Growth" was 50.1; in other words, half of the 

 nutrient material fed has actually gone towards the building up of 

 the body tissues. This result is of much significance, inasmuch as 

 it adds further proof for the idea that neither the utilization of the 

 food in digestion, nor indeed the actual quantity consumed, deter- 

 mines the extent of the resulting growth of the organism. The 

 trout in this experiment increased in weight at a greater rate than 

 in any other of this series, while actually consuming the smallest 

 quantity of food. 



