PROGRESS IN BIOLOGICAL INQUIRIES, 1921. 33 
The study, made in cooperation with the Bureau of Chemistry, 
of the trade-waste problem in its relation to oyster culture was 
continued. Before he left the Bureau Dr. Churchill performed 
experiments with various dilutions of standard solutions of chemi- 
cals known to occur in or to be discharged into water near oyster 
beds. He found the larve very sensitive, certain chemicals being 
fatal even in great dilutions. In Bridgeport Harbor late in the 
season samples were collected for the determination of the distribu- 
tion of injurious wastes, particularly the heavy metals. As a result 
of the study of this harbor and of the efforts of the two bureaus, 
the company, which discharged much the greatest amounts of copper, 
was persuaded to install an electrolytic recovery process, which has 
given great promise both as a money saver and as a means of im- 
proving harbor conditions. 
In June, 1921, the spawning of oysters in Great South Bay has 
been found to begin in earnest almost a month earlier than in pre- 
vious years of our experience and to occur at decidedly lower tem- 
peratures. The work is being so carried on as to check up the data 
obtained in 1919, and already the larvee have been found to be much 
more widely distributed in good numbers. In addition, as oppor- 
tunity permits, data are being gathered to test out the hypothesis 
advanced by Dr. T. C. Nelson that oyster larve of the larger sizes 
keep from being washed to sea by sinking with the ebb tide and 
rising with the flood. 
The study of the development and distribution of the larve is 
of interest to local oystermen and has, it is believed, influenced 
them in determining the times, places, and extent of planting shells 
for set. The immediate purpose of the Bureau, it must be under- 
stood, is to determine the possibilities of the method of larve survey 
in obtaining best results and effecting economies in planting and in 
the prevention of costly wastes from planting in seasons when a set 
is not obtainable. Once a satisfactory demonstration is obtained, 
the method can be appiied in other localities as well as at the places 
where the experiments have been conducted. 
EFFECT OF POLLUTIONS UPON PROPAGATION OF OYSTERS. 
Pollutions may affect oyster eggs and larva, either directly, by the 
toxic effect of certain chemicals upon the young oysters, or indirectly, 
through the exhaustion of the oxygen supply and partial or com- 
plete suffocation of the larvee. The latter aspect of the problem was 
given attention by Dr. P. H. Mitchell, director of the Woods Hole 
(Mass.) Fisheries laboratory. 
In experiments on the effect of oxygen deprivation on oyster larve 
Dr. Mitchell found that while the embryos are sensitive to dimin- 
ished oxygen supply a number of factors affect the lower limit of the 
oxygen content of water compatible with life of the larva. The 
factors noted were: (a) The previous history of the eggs from which 
the larvee were hatched, for example, ripeness at the time of artificial 
fertilization and previous exposure to pollution; (6) the age of the 
larvee; (¢) the carbon-dioxide content of the water; (7) the hydro- 
gen ion concentration of the water; and (e) the temperature. 
Development of a satisfactory technique for handling such un- 
‘usually- sensitive and perishable material as oyster larvae, in the. 
