238 Infestation of Fungus Cultures by Mites 



The great toxic action of Ammonia is not surprising, for it is natural 

 to expect such a strongly irritant substance to be highly poisonous to 

 lower forms of animal life. 



Toxicity of Ammonia and Pyridine to Fungi. 



The toxicity of Pyridine to lower forms of plant life has been the 

 subject of some investigation. The views expressed although somewhat 

 discrepant generally lean towards the opinion of its comparatively low 

 toxic properties. Morgan and Cooper (ii) state that of manv monacid 

 organic bases they tested the bactericidal properties of Pyridine were 

 the least. Lutz(6) has stated that it may act under certain conditions as 

 a food, a conclusion not borne out by the experiments described above, but 

 it must be recognised that very special conditions as to media and organ- 

 ism may be required for the feeding effect of Pyridine to manifest itself. 



Our experiments do not definitely indicate the position of Pyridine 

 in the toxic scale as far as fungi are concerned, but we lean to the view 

 that it is not high. This is not easy to understand, for the compound is 

 inert and its basic properties weak. The latter fact, if theviewsof Newton 

 Harvey (12) are correct, should indicate a rather high toxicity. This in- 

 vestigator points out that weak bases penetrate cell walls with greater 

 rapidity than strong bases such as Caustic Soda, and that penetration 

 is of the first importance in determining toxicity. On the other hand, 

 another important and countervailing factor is dissociation, the least 

 dissociated bases being least toxic. 



As Pyridine is a weak base and very slightly dissociated its toxic 

 properties might be low despite its penetrating power. It is outside the 

 purview of the present investigation to explore this problem, but the 

 rate of penetration of cell walls by chemical compounds is one of funda- 

 mental importance in the consideration of fungicidal and insecticidal 

 problems and further investigation along these lines is contemplated. 

 Our results show that fairly high doses such as -b--^ per cent, of Pvridine 

 may inhibit germination and growth, and it is probable, although no 

 proof is here advanced, that this is due to the Pyridine readily permeating 

 the cell. These spores, however, will grow if the base is neutralised by 

 acid, the Pyridine in all probabihty diffusing out of the cell with readiness 

 as soon as the diffusion gradient is modified in a reverse way by the 

 addition of the acid. Our experiments show that what little toxic pro- 

 perties Pyridine may have, it possesses chiefly in virtue of its basic 

 nature. Its salts are hardly poisonous at all either because the acid ion 

 prevents the migration and penetration of the cell wall by the pyridineum 

 ion, or if the salt of Pyridine does penetrate its toxic properties within 



