THE TOXICITY TO FUNGI OF VARIOUS OILS AND SALTS. 13 
An effort was made to handle them in pure culture under sterile 
conditions. The selection, however, of test organisms which play 
at most but a slight role in the decay of timber is not to be recom- 
mended. As many factors of error as possible should be eliminated 
from such tests, for there are certain to be many remaining after all 
precautions are taken. 
During the same year Rumbold (25) carried out a series of tests with 
different wood preservatives, using agar media in Petri dishes as well 
as toasted bread soaked in the antiseptics. In the case of the agar 
cultures, the media and preservative were mixed before sterilization. 
This procedure is known to lead to very erroneous results with cer- 
tain substances, such as zinc chlorid and copper sulphate. In all 
cases the preservative and media should be sterilized separately 
and heated no higher than is necessary during the mixing, in order 
to avoid as far as possible any chemical combination which tends 
to occur. The higher concentrations of the salts mentioned above 
cause a liquefaction of agar or gelatin media when sterilized together. 
One test conducted in our laboratory showed that zinc chlorid at 0.6 
per cent concentration when sterilized after mixing allowed even 
more growth of Fomes annosus than 0.2 per cent when the two com- 
ponents were not sterilized together. Concentrations of the sterilized 
mixture below about 0.4 per cent appeared to be stimulative, giving 
a white, fluffy growth, which was more luxuriant than in the creamy 
check cultures and which grew up over the under side of the covers 
of the Petri dishes. 
The use of bread for culture media likewise is objectionable, for 
the starch therein contained possibly acts as a diluting agent, as 
already indicated in the discussion of the phenomena of adsorption. 
For instance, in comparing Rumbold's tests of sodium carbonate on 
bread and on agar it is seen that considerably more of the preserva- 
tive is required to check the growth of the organisms when the for- 
mer medium is used. 
In 1912, Falck (7), and Dean and Downs (4), published the results 
of work on various wood preservatives in agar media, using wood- 
rotting organisms. 
The former covered a wide range of possible preservatives (some 
60 or 70), including phenols and cresols and their derivatives, benzol 
derivatives, fluorin compounds, acids, alkalies, and inorganic metal- 
lic salts. The work appears to have been very carefully done and 
is an extremely valuable contribution to the subject. It is open to 
the objection, however, that the tests were of too short a duration. 
Dean and Downs report only a few tests on tar oils in a bean-agar 
medium, using the cosmopolitan wood-rotting fungus Polystictus 
versicolor. These investigators introduced a method of preparing 
creosote emulsions with gum arabic, which was considered advanta- 
