Sources of Error 87 



seeking oxygen. The bacterial cloud at times remains stationary, or 

 moves gradually upward in the fluid, so that clear fluid may be seen 

 above and below. The behaviour of various bacteria under somewhat 

 similar conditions, has been the subject of an interesting investiga- 

 tion by Beyerinck (Ueber Athmungsfiguren beweglicher Bakterien. 

 Centralhl. f. Bakteriol. 1893, xiv. pp. 827—845), who refers to the 

 " Bakterienniveau " as the point in the fluid where the bacterial cloud 

 may hover at times for days. 



See further under medico-legal applications of the precipitin method, 

 Section IX., also p. 63, regarding insoluble bloods. 



