EXPERIMENTAL CONDITIONS 57 



therein. 1 This not unnatural scepticism has been 

 partly due to the fact, as I have previously stated,, 

 that the Bacteria are always motionless, but pro- 

 bably to a far greater extent to a general disbelief 

 in the possibility of " spontaneous generation." 



Such difficulties are, however, easily met. It 

 will be found that the organisms are generally 

 most abundant and most varied in nature in the 

 yellow solutions. But in them there have been no 

 solid ingredients introduced into the tubes only 

 freshly distilled water with a few drops each of 

 dilute sodium silicate and of liquor ferri perni- 

 tratis. While in the colourless solutions the only 

 solid ingredient has been a few grains of ammo- 

 nium phosphate. After the heating process it is 

 true there is a deposit of flakes of silica or of 

 silicate of iron; but examination of portions of 

 these after a few days will reveal no organisms, 

 while an examination of the contents of other 

 similar tubes after some months will probably 

 show numerous motionless organisms (Torulse or 

 Bacteria, or both) on the flakes. But, as I have 

 previously said : " If organisms are not there at 



1 See the report of the discussion which followed the reading 

 of my communication to the Royal Medical and Chirurgical 

 Society of London in the Transactions of that Society (vol. xc., 

 1907, pp. 536-540). 



