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 r61e 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- 



