Sibyl T. Jkwson and F. Tattersfield 237 



9. Discussion of Results. 

 Toxicity of Pyridine and Ammonia to Mites. 



Pyridine is shown to have a considerable toxicity to mites and while 

 its effect upon fungi (in the small doses necessary to kill mites) is prac- 

 tically nil, in continually increasing doses it becomes more marked until 

 a concentration is reached at which germination and growth are com- 

 pletely inhibited. The toxicity to mites is surprising as it has generally 

 been assumed that the toxicological action of Pyridine to all living 

 organisms is not marked. 



Pyridine and the various monacid ammonium bases have been the 

 subject of considerable toxicological research, either because of their 

 occurrence as groups in the molecular structure of many well-known and 

 widely used alkaloids {e.g. Nicotine) or because of their close similarity 

 to them in physiological action. 



Brunton and TunniclifEe(8) have shown that on frogs. Pyridine has, 

 in relatively small doses, a general narcotic action, that its paralysing 

 action on motor nerve endings is of the slightest and that its action is 

 almost wholly confined to the sensory part of the nervous system. They 

 came to the conclusion that Pyridine, compared with its derivatives, is 

 not an active poison, a conclusion that would hardly be expected when 

 the very marked stability of Pyridine is borne in mind. From its close 

 relationship chemically to Nicotine, one would expect a fairly high in- 

 secticidal value, yet Pyridine has proved itself of little use in this respect. 



Fryer (9) states that after a large number of tests the results have 

 proved in all cases disappointing. The Entomologist to the United States 

 Dept. of Agriculture (10) confirms this and reports that while the com- 

 pounds most highly poisonous to insects are to be found among the 

 organic nitrogen derivatives the toxic value of Pyridine is small. 

 Tattersfield and Roberts (3) found that to wireworms, Pyridine was less 

 potent as an insecticide than any other of the organic bases tested. 



Although the present results do not definitely prove that Pyridine is 

 a compound of high specific toxicity to mites, they do indicate that it 

 possesses a toxic action which is much greater than experience would 

 lead us to expect. We were only able to compare it critically with 

 Aniline, a comparison which led to the conclusion that the low vapour 

 pressure of the latter compound tended to put a limit on its toxicity, 

 but that molecule for molecule in the same time it was more poisonous 

 from a quantitative point of view than Pyridine. On the other hand in 

 very minute doses Pyridine had a most profound narcotic effect, inhibit- 

 ing all the larger movements and leading to almost complete paralysis. 



