198 
BULLETIN OF THE BUREAU OF FISHERIES 
showed a retardation by 8-9 percent, while in one experiment the growth in pure 
paraffin and paraffin-oil cultures was increased by 17 percent (fig. 15). 
Indefinite results of the experiments should probably be attributed to the action 
of bacteria which, as has been shown by Hopkins and Chinbal (1932), Buttner (1926), 
Tausson (1927), and Haas (1926), in the absence of more suitable material can grow 
on paraffin and utilize it as their only source of carbon. A great part of our paraffin 
and paraffin-oil cultures showed very abundant bacterial growth. 
Other attempts to incorporate oil in some suitable substance at the bottom of 
culture flasks were unsuccessful. 
EFFECT OF WATER SOLUBLE FRACTION OF OIL 
Two different methods were used in preparing water soluble extracts of oil. 
The first method consisted in stirring together oil and filtered sea water and allowing 
the mixture to stand for various lengths of time. In the second method measured 
amounts of oil were poured in collodioD bags suspended in flasks containing Nitzschia 
culture and the water soluble constituents of the oil gradually diffused through the 
membrane. 
The proportions of oil and water used in preparation of the extracts according 
to the first method as well as the duration of stirring and standing are given in 
table 20. 
Table 20. — Preparation of oil extracts in sea water 
Proportions oil to water 
Hours of 
stirring 
Days of 
standing 
Specific gravity 
of sea water 
(17.5° C./17.5 0 C.) 
Specific gravity 
of extract 
(17.5° C./17.5 0 C.) 
11 
12 
12 
1. 02433 
1. 02400 
12 
2 
2 
1. 02461 
1. 02380 
12 
2 
3 
1. 02435 
1. 02434 
1:2 
12 
10 
1. 02463 
1. 02434 
1:2 
3 
7 
1. 02445 
1. 02448 
The oil was subsequently filtered off and the resulting clear aqueous extract was 
heated to boiling to allow for sterilization. Before sterilizing the specific gravity of 
the extract was determined. In most cases it was slightly lower than that of the 
sea water used. 
The results of these experiments are summarized in table 21 which shows the 
percent of retardation ( — ) or stimulation (+) of growth caused by the addition of 
various concentrations of five different extracts. All the experiments were carried 
out with Lake Pelto oil. The figures are the averages of three or more samples. 
Table 21. — Effect of water soluble fraction of oil on the growth of Nitzschia culture 
[Figures in the body of the table represent percent of retardation (— ) or stimulation (+)] 
The figures given in table 21 represent the end results of experiments which ran 
from 9 to 21 days. Of the 25 experiments with various dilutions of oil extract 6 
