fi.e in eaoh finger bowl, were placed in such a manner as to avoid 

 direct contact with oil. The first experijnents consisted in testing 

 the relative toxicities of crude oil, Diesel oil, and lubricating oil 

 in the concentrations of 1:10, 1 t20, and lj40. The results are 

 sunmarited in tables 13, 14, and 15. Crude oil added in the ratio of 

 lt40 killed three out of five test embryos within 47 l/2 hours. 

 Toxicity of Diesel oil was noticeable within 52 hours in the concentra- 

 tion of 1:20, while lubricating oil was ineffective even in the con- 

 centration of 1:10 (50 hours). 



In view of high toxicity of crude oil, a aeries of tests were 

 made in which the quantities of oil added to the water varied frcen 1:20 

 to 1:200. As the examination of table 16 shows, even the lowest con- 

 centration of 1:200 was sufficiently toxic to kill all five embryos in 

 11 days. The mortality of embryos in greater quantities of oil was 

 more rapid. There was no death among the controls. 



The relationship between the time of death and the quantity of 

 oil used is shown in figure 1. The- open circle curve, forming the lower 

 limit of the bend, corresponds to the time of the first death i the dark 

 circles to the time required to kill all five onbryos. Thus, the lower 

 and upper boundaries of the band represent respectively the relationship 

 between the qnantity of oil used and the time of survival of the weakest 

 and the hardiest specimens. 



If the log of the survival time is plotted against the log of con- 

 centration, the toxicity curve approximates a straight line (fig, 2). 

 fhe linear relationship obtained by such plotting can be approximately 

 represented by a general equation of the ■type y = a x " and the 

 constants a and c may be computed from the empirical data. We see no 

 parti oular""advan'fege at present in making these computations, since the 

 nature of toxio substance extracted from oil is not known. It is, how- 

 ever, significant that the relationship between the time of survival of 

 embryos and the cfoantities of oil used follows the tj^Je of a time- 

 concentration curve typical for a number of coal tar disinfectants, 

 phenol and other toxic substances (Clark, 1933) • 



Tests with different types of oil showed that, as in the experiments 

 with Tubularia and barnacles, ihe crude oil was the most toxic. All the 

 tests were made using the oil in ratio of 1 part to 40 parts of sea water 

 (table 17) and keeping the embryos exposed for five days. No toxic effect 

 was noticeable in the water containing lubricating oil. 



EXPERIMENTS WITH HARD SHELL CLAMS, VENUS MERCENARIA LINN 



The hard shell clam, Venus teroenaria , ohosen for experiments because 

 of its economic value, is frequently found in polluted bottans of harbors 

 and bays. Because of their ability to close themselves within their shells. 



21 



