40 American Fisheries Society 



separately. In the course of the first month, it will be seen, the 

 trout gained 77.3 per cent in weight. It consumed 85.34 grams 

 of beef heart, and the excretion from day to day showed remark- 

 able constancy. It will be noted also that the amount of nitrogen 

 in the feces was almost invariably 10 per cent of the dry fecal 

 matter, and this proportion coincides with that found in the feces 

 of mammals on a pure meat diet. The dry feces constituted about 

 5 per cent (Table VI) of the dry material ingested with the food. 

 The utilization of the food — protein and fat — has been almost con- 

 stant throughout this part of the experiment. Of the 2.8981 grams 

 of nitrogen fed, 0.9329 grams was retained. In the absence of exper- 

 iments on the respiratory exchange, the retention of fat could not, 

 of course, be worked out. Considering the amount lost with the 

 feces, 96.1 per cent of the consumed protein was utilized, and 94.5 

 per cent of the fat. Not only has the utilization of the food through 

 digestion been good, but as the " Index of Growth " (ratio between 

 increase in weight and quantity of consumed food per kilogram 

 and twenty-four hours) will show, it furnished a considerable 

 proportion of its material to the building up of the body tissues. 

 The consumption of the trout per day and kilogram of weight 

 amounted to 37.5 grams of food, while the increase in body weight 

 per day and kilogram was 17.4 grams. In other words, 46.5 

 per cent of the food material was added to the organism (See 

 Table VI). The trout was then allowed to fast for a fortnight, 

 (F-4, Table I), in order to find out how this would affect the 

 digestive power and general condition of the animal whose 

 metabolic exchange had been carefully established by the previous 

 study. 



Upon resuming feeding, the trout gained 15.7 per cent in two 

 weeks. During the first four days of re-alimentation, the very 

 small amount of nitrogen in the water (urine) is very marked. 

 During the first part of the experiment, the urinary nitrogen 

 represented on the average 63.9 per cent of the total nitrogen 

 consumption, but during the first and second forty-eight hours 

 following the fast, it was 39.7 and 57.2 per cent respectively. 

 There was thus undoubtedly a retention of nitrogen. As the 

 elimination for the next forty-eight hours shows, this this reten- 

 tion was only temporary. 



