236 Infestation of Fungus Cultures by Mites 



As previously stated it was considered that these results might be 

 due to the alteration in 7>H values of the medium on the addition of 

 Pyridine. The medium used has a pH value of about 4-75, which the 

 addition of -429 per cent, of Pyridine brought up to 6-45. To test this 

 point a series of experiments was set up in which the ^H's of the medium 

 were adjusted by means of ^7^^ Sodium Hydrate to those obtained in 

 the flasks in which the higher concentrations of Pyridine inhibited 

 growth. It will be seen from Table X that the effect of increasing the 

 ^H from 4-75 to 6-55 is very small. The alteration of joH plays, therefore, 

 an insignificant part. One other interesting point arising from these 

 experiments is that the effect of Pyridine is to inhibit the germination 

 of the spores rather than to kill, at any rate all of them, outright. After 

 the yields in Series III, Table IX, had been weighed, additions of standard 

 sulphuric acid were made to the flasks 21-27 where no growth was visible: 

 within two days the spores in these flasks had begun to germinate and 

 growth took place at a rapid rate. After standing for three weeks the 

 yields were weighed, the results being set forth in the last column of 

 Table IX. They are of the same order as those given by the controls 

 during the previous three weeks. At the end of this period the Pyridine 

 remaining in two of the experiments (19 and 27) was determined. The 

 amounts found are expressed in brackets in column 4. 



Lutz (6) has stated that in the presence of some other form of assimi- 

 lable nitrogen, Pyridine may act as a food to fungi. Although our experi- 

 ments were not set up to investigate this point and must not be regarded 

 as final, for this particular fungus {Aspergillus niger) we have not 

 obtained any evidence of Pyridine acting as a stimulant to fungal growth. 

 However small an addition of this base might be made there has never 

 been shown an increase in the yield which could be considered outside 

 the margin of error of the experiment. There is undoubtedly towards the 

 end of the series in Table IX a loss of Pyridine, which however cannot be 

 accounted for by assimilation, being probably due to volatilisation as it 

 is greater as the amount of growth diminishes. Moreover, the deficiency 

 in the amount of Pyridine found after its neutralisation and allowing 

 the Aspergillus to grow for a further three weeks is of the same order 

 as that found in the flasks where at the end of three weeks and before 

 neutralisation the growth had been small. 



The amount of Pyridine absorbed by culture media from an atmo- 

 sphere saturated with its vapour is about 4 per cent, in sixteen hours. 

 This is much more than a toxic dose. Subculturing after treatment, 

 especially of fungi growing in liquid media, is therefore essential. 



