THE TOXICITY TO FUNGI OF VARIOUS OILS AND SALTS. 5 



cently reported the effect of about 50 different salts and acids upon 

 yeasts, as compared with other organisms, and has found them gen- 

 erally to be more resistant than algse or flowering plants. Silver 

 nitrate, which is very deadly to many molds, bacteria, and algae (the 

 bacterium Staphylococcus pyogenes requiring only 0.0002 per cent to 

 check growth; the alg?e, Spirogyra and Cladophora, only 0.0001 per 

 cent), will not kill yeast until the concentration reaches 0.001 per 

 cent. Similarly, mercuric chlorid is toxic to Spirogyra in a 0.000001 

 per cent solution, but a 0.01 per cent solution is required to kill beer 

 yeast. 



Molds. — The common molds, such as Penicillium, Aspergillus, 

 Sterigmatocystis, and others, taken as a whole, are highly resistant 

 to toxic agents as compared with the true wood-destroying fungi. 



Whereas much experimental work has been done on the former, 

 comparatively little has been carried out on the latter group. 



The so-called Penicillium glaucum Link., which in the light of 

 recent work has been shown to consist of a group of several distinct 

 species of Penicillium, to which the composite name was indiscrimi- 

 nately applied, is one of the most resistant molds recorded. Pulst 

 (23), Clark (3), and Gueguen (10) all agree that from 16 to 21 per 

 cent of copper sulphate is required to stop its growth, and Pulst 

 claims that it will even germinate and fruit in a 33 per cent solution 

 of this salt or a 38 per cent solution of zinc sulphate if allowed to 

 develop a sufficiently long time, i. e., from three to five months. 



Clark (3) has tested the' effect of some 28 salts and acids upon four 

 or five of the common molds, the tests being made in hanging drop 

 cultures of beet infusion. His table of toxicities indicates that such 

 salts as mercuric chlorid, potassium bichromate, silver nitrate, and 

 potassium chromate are approximately 400 times as effective against 

 these organisms as copper sulphate, sulphuric acid, hydrochloric 

 acid, and zinc sulphate, the comparison being based on molecular 

 solutions. 



EFFECT OF COMPOSITION OF MEDIUM ON TOXICITY. 



The toxicity of a substance may vary for the same organism when 

 culture media of different compositions are employed. This is due, 

 in large part, to the chemical or physical affinity of some substances 

 for certain constituents of the media, or possibly to some change in the 

 permeability of the plant protoplasm. The well-known reaction 

 of some copper salts with sugars and of mercuric chlorid with albumi- 

 nous compounds, or the effect of adsorption will serve to illustrate 

 the point. 



The most careful work on toxicity has been conducted, using pure 

 distilled water as a medium. However, the use of this method with 

 fungi is practically limited to the germination of spores; nutrient 



