Sibyl T. Jewson and F. Tatterspield 231 



crucibles and fungus were then dried for 24 hours at 70° C. and finally 

 at 90°-100° C. to constant weight. 



The technique of the method has not yet been completely studied 

 by us, but it proved of sufficient accuracy for the purpose of this investi- 

 gation. Experiment No. 1 was carried out on an Aspergillus sp. isolated 

 from an onion. The cultures were incubated at 26° C. for a period of 

 seven days. Table VII shows that the growth of this fungus is not 

 inhibited until a concentration somewhere betAveen -318 and -636 per 

 cent, of Pyridine is reached. 



Table VII. 

 Effect of Pyridine on Aspergillus niger. 



Culture solution Coons' double strength 200 c.c. Temp. 26° C. 



Crop yield 

 after 

 Description Remarks after 3 days 7 days 



1. -159 %=-002 gm. mol. Pyridine per 100 c.c. Growth equal to con- -3914 gm. 



trol 



2. -318% = -004 „ „ „ Reduced growth; small -4044 „ 



colonies 



3. -636% =-008 „ „ „ No growth No growth 



4. 1-272% =-016 „ „ „ No growth No growth 



5. Control Good growth -3536 gm. 



6. 



•3845 



7. „ „ -3942 „ 



8. " „ -3620 „ 



It was desirable to ascertain whether the toxicity of Pyridine was 

 due to its possessing basic properties either acting directly or indirectly 

 by its effect upon the pH value of the medium. Two sets of flasks were 

 used. One set contained gradually increasing doses of pure Pyridine as 

 in the previous experiment, but in this case starting with -318 per cent, 

 of this compound (=-004: gm.-mol. per 100 c.c.) and working up by 

 smaller increases to -636 per cent. The quantities of Pyridine in the 

 second set exactly talhed with those in the first except that before 

 addition the Pyridine solution was brought to a pK value of about 4-7 

 (the same as the medium) by the addition of appropriate amounts of 

 standard sulphuric acid. The culture of Asp. niger used was one kindly 

 given to us by the Pure Culture Laboratory at the Lister Institute, 

 No. 594, grown on Czapek's medium and about 7 days old. It proved, 

 unfortunately, rather more susceptible to poison than the one used in 

 the previous test. After inoculation the flasks were set aside in a dark 

 cellar, the temperature of which remained somewhere between 18-5° C. 

 and 19-5° C. Recourse was had to a rather lower temperature as there 



