PROGRESS IN BIOLOGICAL INQUIRIES, 19 31 519 



chosen was oflPshore and avorajied 16 feet deep. The starfish were 

 small, ranfjing in size f"om 3 to 6 centimeters, and were very numer- 

 ous. The same type of experiment as before was tried, except that a 

 12-foot 114-inch brass pipe was used to form horizontal bar of the 

 T and the T connected by a large hose to the bilge pump of the steam 

 boat. One hundred fifteen gallons of solution containing 100 pounds 

 of copper sulphate and 75 pounds of nitre cake were placed in vats 

 on the deck. The nitre cake is a crude sodium acid sulphate contain- 

 ing a high percentage of sulphuric acid and serves to make the solu^ 

 tion more acid, and consequently retards the reaction of the copper 

 with the sea water. 



The solution was pumped out at slack low tide on August 17, 

 along a straight line of 500 feet. Twelve minutes pumping emptied 

 the vat. The original pH was 7.8 and the copper content 0.1 part 

 per million. Immediately following the treatment the pH value 

 had dropped to 7.2, but the copper content showed only 0.7 part per 

 million. Next day there were practically no ill effects noticed on 

 the starfish. In three dredges bringing up 33 starfish after a minute's 

 hauling there were only 4 dead ones. The pH and copper content had 

 returned to normal. Better results were obtained in the experiments 

 on grounds of the Beacon Oyster Co., at Wickford, K. I. 



A summary of the results of numerous experiments brings out the 

 following points : 



(1) Copper sulphate in no case killed more than 10 per cent of 

 the starfish. 



(2) Application as a solution is to elaborate in manipulation and 

 no more effective than crystals. 



(3) The most effective application consists in scattering crystals 

 of copper sulphate at slack low water, preferably at neap tide. 



(4) Starfish reaction to the presence of copper sulphate is one of 

 avoiding the treated area. 



(5) The use of paper bags filled with crystals presents a more 

 accurate and economical method of application. 



(6) Only in one case were there indications of death of the oysters. 

 Periodic treatment did not seem to affect the food supply to such 

 an extent that the oysters were harmed. 



Because of the difficulties encountered in killing adult starfishes by 

 copper-sulphate treatment, it is expected that the solution of the 

 problem can be found in the control of propagation of starfishes 

 rather than in destroying the adults. 



PACIFIC COAST OYSTER STUDIES 



At the Hopkins Marine Station, Pacific Grove, Calif., experiments 

 were made by Dr. A. E. Hopkins during three months on the sensi- 

 tivity of the oyster to salts, most of which normally occur in sea 

 water. The chemical sense of the oyster is highly developed, as 

 shown by the following threshold concentrations: Potassium sul- 

 phate, M/640; potassium ferricyanide, M/25,000; potassium nitrate, 

 M/40.000. The potassium salts activate the oj^ster more effectively 

 than the salts of any of the other normally occurring cations. 



/Studies of oyster culture in Puget Sound. — An intensive investiga- 

 tion was begun during 1931 in cooperation with the State of Wash- 



128210—32 6 



