372 U.S. BUREAU OF FISHERIES 



ments represent relatively crude assays but they provide the founda- 

 tion for improved ones. 



After the first experiments with trout feeding, a requirement for 

 specific substances similar to vitamins was recognized by Dr. McCay. 

 This vitamin requirement could not be stated in terms of recognized 

 accessory factors since it was very sensitive to heating and was de- 

 stroyed when food prcjducts were dried at the usual high tempera- 

 tures in contact with air. 



In the course of the past 3 years, it has been discovered that 

 this vitamin termed factor H is partially preserved by drying at 

 low temperatures in contact with an inert gas. Since the determina- 

 tion of the requirements of trout for the recognized vitamins is very 

 difficult until more is learned concerning the nature of factor H, 

 efforts have been continued to prepare a concentrated extract con- 

 taining this growth factor. 



Two methods of testing have been employed. One consists in 

 feeding trout on a purified mixture of casein, a starch-dextrin, yeast, 

 cod-liA^er oil, and salt mixture, plus the supplement to supply factor 

 H. Yeast and cod-liver oil have been used simply because it is very 

 likely that all higher animals require some of the factors contained 

 in yeast as well as some of the fat soluble vitamins. 



Up to the j)resent time only alcoholic extracts of beef lungs and 

 liver have been prepared. Careful methods have been employed in 

 order to preserve the accessory growth factor. Dried beef liver, 

 evaporated in vacue under inert gas, was prepared as a control. 



From a number of assays it was found that 15 percent of raw 

 liver was an adequate supplement for an otherwise complete diet, 

 furnishing a sufficient supply of factor H. Hence, the present ex- 

 periments were started with a 5 percent supplement on concen- 

 trated products, but growth and mortality curves show that this 

 level was too low. At the end of about 2 months the supplement 

 was increased to 15 percent. Nevertheless, growth curves indicate 

 that much of the original growth factor was lost even in the vacuum 

 dried liver. It also indicated that a considerable fraction of factor 

 H is held in the alcoholic extract. The lung residue is almost totally 

 lacking in this factor, while the liver residue still retains some 

 potency. 



A second series of assays were undertaken, testing the efficiency 

 of autolyzed liver products as supplements for a synthetic diet de- 

 ficient in factor H, in the hopes of finding a liquid liver with a high 

 degree of potency. These data indicate that raw egg and liver ex- 

 tract, plus residue, have considerable amounts of factor H, but they 

 do not clearly establish that autolysis destroys factor H because 

 the material used as a preservative in the course of autolysis may 

 have influenced the results. 



LIMNOLOGICAL INVESTIGATIONS IN THE ROCKY MOUNTAIN 

 REGION IN THE INTEREST OF EISH STOCKING 



Because of the severe curtailment of the Bureau's appropriations, 

 investigations in the national parks and forests under the direction 

 of Dr. "a. S. Hazzard were omitted during 1983, and a program of 

 field work which entailed minor expenditu.res was substituted. How- 

 ever, lessened field activities afforded opportunity for study of data 



