74. U. S. BURHAU OF FISHERIES 
organisms. As the biochemical and physiological tests are quite 
exacting, each fish is maintained and studied as a separate patient, 
frequently for a period of several months. More than 200 such fish 
are under observation at Columbia, and upwards of 500 catfish are 
being studied as part of this investigation at Fort Worth. ‘These 
studies have progressed to the point where it is possible to conclude 
that there is impairment of the growth and nutrition of fishes in 
waters treated with even small quantities of arsenicals and several 
other materials commonly used as mosquito larvacides. A separate 
report on this subject will be prepared early in 19389. 
During the latter part of the year physiological studies were begun 
to determine the effects of several substances dangerous to fish life 
which were found in natural waters in the West in the course of the 
summer’s field investigations. These studies are being carried out in 
both the Columbia and Fort Worth Laboratories. 
Summer field, surveys —During the summer of 1938 intensive 
studies of stream pollution were made throughout the greater part 
of Western United States, and many new data were collected on the 
nature and effects of polluted waters. Observations were made in 
the States of Texas, Arizona, Nevada, California, New Mexico, 
Oregon, Washington, Idaho, Wyoming, Montana, Minnesota, North 
Dakota, and Nebraska. About 5,000 analyses were made in the field 
and additional material was returned to the laboratory at Columbia, 
Mo., for further analysis. ; 
After leaving Columbia early in the summer, Dr. Ellis and field 
party proceeded to the Fort Worth (Tex.) Laboratory where par- 
ticular attention was given to the catfish investigations In progress 
there. From Fort Worth the party proceeded to Uvalde, Tex., 
where a study of water conditions indicated the source of at least 
one of the difficulties hampering pond operations, not only at Uvalde 
but also throughout the Southwest. While in Texas, the party had 
an opportunity to make direct observations on the silt and salt loads 
of floodwaters, obtaining valuable data. 
Studies of impounded waters continued at Elephant Butte Reser- 
voir in cooperation with the United States Reclamation Service and 
the National Research Council, and at Lake Mead in cooperation 
with the same agencies and the National Park Service. At Elephant 
Butte opportunity was afforded to use a new piece of apparatus 
recently developed in the Columbia Laboratories by means of which 
direct determinations of silt, turbidity, water temperature, and light 
transmission were possible inch by inch throughout the entire depth 
of the lake. This new apparatus gave valuable detailed data con- 
firming previous observations made by less accurate methods. Ap- 
plication of various new methods and pieces of apparatus to surveys 
of these western impounded waters is proving very profitable and 
is providing a wealth of new information on water problems which 
has not been available previously. A manuscript on Lake Mead is 
planned, comparable to the one on Elephant Butte now nearing 
completion. 
After completing the work at Lake Mead the party proceeded to 
the geyser fields and the Hot Creek region in California where a 
large series of observations were made. At Gold Beach, Oreg., work 
carried on during the previous summer on the Rogue River mining 
problems was checked and extended. 
