EFFECT OF CRUDE OIL POLLUTION ON OYSTERS 
193 
The results of 13 experiments may be summarized as follows: 
1. Oysters subjected to several treatments of oil extract or bleed water do not 
develop higher tolerance to oil extract or bleed water in concentrations used, or within 
the time limits studied. 
2. Particularly in the case of oil extract, the second and succeeding treatments 
have a less immediate but more prolonged retarding effect on the rate of pumping. 
3. There is no evidence of permanent injury caused by this treatment. Re- 
covery is usually complete. 
EFFECT OF CRUDE OIL ON DIATOMS 
By Paul S. Galtsoff and Vera Koehring 
Since diatoms invariably appear to be constituents of the oyster diet, their rate 
of growth in the medium to which various polluting substances were added, may be 
taken as an index of the effect of pollutant upon the food supply of the oyster. In 
the regions where oysters grow, diatoms are usually distributed throughout the water, 
in the surface layers as well as on the bottom. Oil in water may affect their growth 
by forming a surface film which may interfere with the gaseous exchange between 
air and water or by the toxic action of water soluble constituents of the oil. It has 
been demonstrated by Lord Raileigh (1923) and Langmuir (1916, 1917) that the 
spreading of an oil upon water is due to the active carboxyl group of the oil molecule 
which because of its great affinity to water readily goes in solution, whereas the 
hydrocarbons having far greater attraction for one another than for the water, remain 
insoluble. By spreading into a monomolecular fi lm the carboxyl groups combine 
with water without causing the separation of the hydrocarbon chains. Hence, a 
pure hydrocarbon oil, as has been demonstrated by Hardy (1912, 1919) for benzene 
and cymene, fails to spread. In case of oil in the natural waters the problem is more 
complex because we are usually dealing with mixed oils which, upon being exposed 
to air, change their chemical properties. Oxidized samples of oil, according to 
Hacker (1925), have an increased spreading power, and chemically inert hydrocar- 
bons upon acquiring certain radicles, —OH, — O, —COO, and — NH 2 , have an at- 
traction for water. For a detailed discussion of this problem the reader must consult 
the original papers of the above-mentioned authors, whose findings are briefly men- 
tioned here only as an illustration of the possible changes in the solubility and behav- 
ior of crude oil in water, which may account either for the formation of blobs or for 
the unchecked spread of oil film over a great area of the sea. A comprehensive in- 
vestigation of the problem would require extensive chemical studies of the oil before 
and after its discharge into the sea, which the authors were not in a position to under- 
take although they fully realized the necessity of such a study for the solution of the 
oil pollution problem. 
Oil discharged into the sea does not remain on the surface. Part of it is absorbed 
by the colloidal particles of clay present in the water and is gradually settled on the 
bottom. This can be seen in both the aquaria tanks in which oil-polluted sea water 
is kept and in many sections of the coastal waters affected by pollution. In a com- 
paratively short period of time considerable quantities of oil floating in the water is 
found absorbed and deposited on the mud bottom from which it can be separated 
by squeezing and decanting. Mud contaminated with oil may be considered as a 
possible source from which water soluble constituents of the oil gradually go into 
solution even after a complete disappearance of oil from the surface. 
