M or gulls. — Studies on Fish Nutrition 41 



During this third two-day period, the urinary nitrogen repre- 

 sented 106.1 per cent of the consumed nitrogen. In other words, 

 the nitrogen ingested since the fast was broken, was not excreted 

 until six days later. The nitrogen elimination then gradually 

 diminished, but even after two weeks, it was still 10 per cent 

 higher than in the first part of this experiment. 



An examination of the feces also revealed that the amount of 

 dry excreta has become 50 per cent greater than during the pre- 

 ceding period, and furthermore that the feces became very fatty, 

 in fact from the fifth until the tenth day of resumed feeding, the 

 per cent of fat was extremely high; this apparently being due to 

 delayed elimination of undigested fat rather than to a progressive 

 impoverishment of the digestive functions. In this respect there is 

 almost a direct relationship to the excretion of urinary nitrogen. 

 The utilization of nitrogen during these two weeks was 94.8 per 

 cent, not essentially different from the degree of utilization in the 

 pre-fasting period, but the fat utilization was only 91.7 per cent. 



That the general condition of the trout was impaired by the 

 starvation, is indicated best by the lowering of the "growth 

 index" (See Table VI). During these fifteen days the trout 

 received 26.7 grams of raw beef heart per day and kilogram of 

 body weight, but it gained only 9.73 grams in weight; in other 

 words, the "growth index" was 36.5 per cent as compared to 

 46.5 per cent of the earlier part of the experiment. 



The experiment recorded in the next table presents much 

 similarity to the preceding one. Six small fingerlings weighing all 

 together only 33.6 grams, were used. During the first part of the 

 experiment lasting twenty-six days, these small trout were fed thir- 

 teen times and the excreta were collected and separately analyzed 

 four times during that period. A glance at the tabulary summary 

 (III) of the results will show that the animals consumed 25.41 

 grams of the raw beef heart, and gained 11.13 grams in weight. The 

 quantity of dry feces eliminated in that time was 3.52 per cent of 

 the total dry ingested food, and contained 21.2 mg. of nitrogen. 

 The protein of the food, therefore, was utilized to the extent of 97.5 

 per cent, and the fat 96.2 per cent. The "index of growth " was 42.7 

 showing that the fingerlings were growing at a favorable rate. 



Owing to the accidental death of one of the experimental 

 animals, the experiment was renewed with the five remaining 



