PROGRESS IN BIOLOGICAL IITQUIRIES, 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 larvae 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 larvse 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 larvae of the larger sizes 

 keep from being washed to sea by sinldng with the ebb tide and 

 rising with the flood. 



The study of the development and distribution of the larvse 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 larvae 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 applied 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 larvae, 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 larvae. 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 larvae 

 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 larvae. The 

 factors noted were : (a) The previous history of the eggs from which 

 the larvae were hatched, for example, ripeness at the time of artificial 

 fertilization and previous exposure to pollution; (b) the age of the 

 larvae; (c) the carbon-dioxide content of the water; (d) 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. 



