210 U. S. BUREAU OF FISHERIES 
Because of the importance of this problem to all food industries, 
numerous methods have been proposed for measuring or following the 
progress of incipient rancidity. One of the most popular tests is that 
predicated upon the assumption that peroxides are formed as an 
intermediate step in the development of rancid products and such 
peroxide compounds break down in the presence of potassium iodide 
with the liberation of iodine, which can be easily measured. However, 
when the test, as prescribed for other fatty materials, is applied to 
highly unsaturated fish oils, the results obtained are not entirely 
satisfactory. Data are frequently inconsistent and the values ob- 
tained appear to be affected by a number of factors which tend to 
decrease the sensitivity of measurement. In spite of these drawbacks, 
the method has considerable merit on account of its simplicity, the 
speed with which determinations can be made, and the fact that no 
complicated or expensive apparatus is required. Therefore, an 
investigation was undertaken to determine the possibility of improving 
the peroxide test so that 1t could be used as a more reliable tool in 
investigating oxidative deterioration in fishery products. The 
progress of the work so far has been most encouraging. Numerous 
conditions of the reactions have been investigated and a modified 
procedure has been devised whereby a number of the drawbacks of 
other procedures are eliminated. The test, however, must be sub- 
jected to more rigorous examination before definite conclusions can 
be made. Should these studies result in a more effective measure of 
incipient rancidity, future investigations, both scientific and practical, 
on the handling and preservation of fatty fish will be greatly facilitated. 
UTILIZATION OF FISH LIVERS AND VISCERAL ORGANS 
The sustained commercial interest In sources of concentrated 
vitamins A and D has led to increasing demands upon the Bureau for 
information regarding the utilization of fish livers and visceral organs. 
In recent reports reference has been made regarding the development 
~ of methods for extracting oil or vitamins from various types of material 
which would not respond to normal treatment. As a result of the 
data obtained, the Bureau’s technologists have been able to advise 
with the industry on extraction problems and have contributed ma- 
terially to the expansion in vitamin oil manufacture. 
During the past year attention has been directed to a general — 
survey of the potential value of the liver and viscera from all types of 
food fish taken on the Pacific coast. Analyses for oil content and 
vitamin A potency have been made on periodic samples involving 22 
different species of fish. The oil content of the livers from the species 
examined ranged from 1.5 to 35 percent and the vitamin A potency 
of the extracted oil varied from 6,000 to 380,000 units per gram. 
Viscera less liver and stomachs ranged in oil content from 0.3 to 45.3 
percent and yielded oils having vitamin A potencies ranging from 
4,500 to 450,000 units per gram. The data will be summarized for 
publication when the survey is completed. 
PREPARATION OF FISH MEALS OF IMPROVED NUTRITIONAL VALUE 
The Bureau’s interest in fish meal in animal feeding pertains to both 
terrestial and aquatic animals. During the year technologists of the 
Division have continued to cooperate with the Department of Poultry 
