EFFECT OF CRUDE OIL POLLUTION ON OYSTERS 
197 
appears dark, whereas tlie flask on the right containing culture covered with oil had 
few diatoms, thus appearing much lighter. 
All the experiments indicate that a heavy, unbroken surface layer of oil inhibits 
diatom growth when oil remains on the surface for a week and longer. 
EFFECT OF OIL HELD ON THE BOTTOM 
In attempting to devise a method whereby oil could be held at the bottom of the 
flask and would not interfere with the photoelectric measurements the following pro- 
cedure was developed. Four grams of paraffin, melting point 52° to 55 ° C., was mixed 
with 6 drops of oil. The resulting mass, oily to the touch, and having a strong odor, 
Figube 12. — Growth of Nitzschia culture under heavy layer of Pelto oil. 
was sterilized at 150° C. and allowed to cool on the bottom of each flask and strongly 
adhering to it. Pure paraffin controls were prepared in the same manner. The 
flasks were filled with the standard Miquel medium, inoculated with Nitzschia and 
measured at regular intervals. The results of the experiments were, unfortunately, 
inconclusive. In three experiments the growth of Nitzschia in experimental flasks 
was retarded from 4 to 16 percent (fig. 14), as compared with their growth in pure 
sea water. In tln-ee other experiments there was a noticeable stimulating effect 
varying from 17 to 27 percent. Pure paraffin controls also produced inconsistent 
results. In one experiment in 13 days the number of diatoms reached exactly the 
same number as in the plain sea water. In other experiments the paraffin cultures 
