1932 ANNUAL REPORT. 1931 53 



The results obtained in the second series checked up very- well with those 

 of the first wherever experiments were duplicated. The food equivalents were 

 slightly lower in these duplications but this may be due to more efficient feeding 

 with the older fingerlings. Ration E when used as a complete diet gave instructive 

 information. Feeding was begun on July 21st and although the fish did not 

 do well the mortality remained very low until about the last of August when 

 it rose rapidly, so much, in fact, that a change was decided upon. Beef liver 

 was then added, changing the diet to that of number 9. After two days no 

 more deaths occurred and the fish did well to the end. These results support 

 those obtained from diet number 9 and taken as a whole in conjunction with 

 those from beef liver, show that ration E and beef liver may be considered 

 complementary foods and that taken together they constitute an efficient and 

 economical diet for brook trout fingerlings. 



A second series of experiments was conducted by G. A. Mc\^icar following 

 that of R. D. H. Heard of the previous year. A brief abstract of Mr. AlcVicar's 

 valuable findings is as follows: 



Renewed observations were made on the effect of various proteins in the 

 diets, and on the activation of a basal diet with extracts and extraction residues 

 from fresh liver. Additional studies were made with some other foods. 



In each experimental trough twenty selected brook trout were used. The 

 troughs were adequately supplied with fresh water and were cleaned once a 

 day. The fish were fed regularly four times a day. 



Addition of alcohol and acetone extracts of fresh liver and the residue 

 from the alcohol extraction were found to give increased growth, comparable 

 to that produced by a supplement of raw liver, when added at a 20 per cent 

 level to a basal diet consisting of casein 20 per cent., starch 70 per cent., and 

 mineral salts 5 per cent. Negative results were obtained with ether extracts, 

 ether and acetone residues. In the preparation of these liver fractions tempera- 

 tures above 37.5° C. were not used to avoid destruction of any thermo-labile 

 "Factor H" present. 



In common with R. D. H. Heard, who performed these e.xperiments the 

 previous summer, the beneficial eff"ects of these liver fractions are not considered 

 due to their content of Factor H but to presence in the extract of some protein 

 or other food material not provided by the basal diet. Mr. Heard, in his final 

 report, points out that addition of dried liver also in the long run activated 

 the basal diet to a similar extent. This view is supported by additional experi- 

 ments in which the liver extracts were added to a basal diet of dried liver, and 

 caused no marked activation, although raw liver did. The dried liver presumably 

 lacks only the Factor H of fresh liver, and the liver extracts failed to supply 

 this. 



Additional experiments with other foods as supplements to this dried liver 

 basal diet showed that hog melts or calf thymus did not cause activation, while 

 salmon egg meal or yeast supplements did show activating properties. Yeast 

 and salmon egg meal apparently supply appreciable amounts of Factor H. 



Experiments with protein diets showed again that gelatin or albumen were 

 totally inadequate as the sole protein of a diet. It was not found possible, 

 however, to confirm Mr. Heard's findings that these two proteins improved the 

 basal diet of casein, starch and mineral salts to any extent. 



Additional experiments with dried skim milk as a basal diet showed no 

 marked increase with gelatin as a supplement. Dried skim milk itself gives 

 poor growth, but low mortality, and seems of value as a basal diet in these 

 protein experiments. A very marked increase in growth was caused by addition 



